=============
0.9 Changelog
=============

.. changelog_imports::

    .. include:: changelog_08.rst
        :start-line: 5

    .. include:: changelog_07.rst
        :start-line: 5

.. _unreleased_changelog::
    :version: 0.9.11

    .. change::
        :tags: bug, oracle, py3k
        :tickets: 3491
        :versions: 1.0.9

        Fixed support for cx_Oracle version 5.2, which was tripping
        up SQLAlchemy's version detection under Python 3 and inadvertently
        not using the correct unicode mode for Python 3.  This would cause
        issues such as bound variables mis-interpreted as NULL and rows
        silently not being returned.

    .. change::
        :tags: bug, engine
        :tickets: 3497
        :versions: 1.0.8

        Fixed critical issue whereby the pool "checkout" event handler
        may be called against a stale connection without the "connect"
        event handler having been called, in the case where the pool
        attempted to reconnect after being invalidated and failed; the stale
        connection would remain present and would be used on a subsequent
        attempt.  This issue has a greater impact in the 1.0 series subsequent
        to 1.0.2, as it also delivers a blanked-out ``.info`` dictionary to
        the event handler; prior to 1.0.2 the ``.info`` dictionary is still
        the previous one.

.. changelog::
    :version: 0.9.10
    :released: July 22, 2015

    .. change::
        :tags: bug, sqlite
        :tickets: 3495
        :versions: 1.0.8

        Fixed bug in SQLite dialect where reflection of UNIQUE constraints
        that included non-alphabetic characters in the names, like dots or
        spaces, would not be reflected with their name.

    .. change::
        :tags: feature, sql
        :tickets: 3418
        :versions: 1.0.5

        Added official support for a CTE used by the SELECT present
        inside of :meth:`.Insert.from_select`.  This behavior worked
        accidentally up until 0.9.9, when it no longer worked due to
        unrelated changes as part of :ticket:`3248`.   Note that this
        is the rendering of the WITH clause after the INSERT, before the
        SELECT; the full functionality of CTEs rendered at the top
        level of INSERT, UPDATE, DELETE is a new feature targeted for a
        later release.

    .. change::
        :tags: bug, ext
        :tickets: 3408
        :versions: 1.0.4

        Fixed bug where when using extended attribute instrumentation system,
        the correct exception would not be raised when :func:`.class_mapper`
        were called with an invalid input that also happened to not
        be weak referencable, such as an integer.

    .. change::
        :tags: bug, tests, pypy
        :tickets: 3406
        :versions: 1.0.4

        Fixed an import that prevented "pypy setup.py test" from working
        correctly.

    .. change::
        :tags: bug, engine
        :tickets: 3375
        :versions: 1.0.1

        Added the string value ``"none"`` to those accepted by the
        :paramref:`.Pool.reset_on_return` parameter as a synonym for ``None``,
        so that string values can be used for all settings, allowing
        utilities like :func:`.engine_from_config` to be usable without
        issue.

    .. change::
        :tags: bug, sql
        :tickets: 3362
        :versions: 1.0.0

        Fixed issue where a :class:`.MetaData` object that used a naming
        convention would not properly work with pickle.  The attribute was
        skipped leading to inconsistencies and failures if the unpickled
        :class:`.MetaData` object were used to base additional tables
        from.

    .. change::
        :tags: bug, postgresql
        :tickets: 3354
        :versions: 1.0.0

        Fixed a long-standing bug where the :class:`.Enum` type as used
        with the psycopg2 dialect in conjunction with non-ascii values
        and ``native_enum=False`` would fail to decode return results properly.
        This stemmed from when the PG :class:`.postgresql.ENUM` type used
        to be a standalone type without a "non native" option.

    .. change::
        :tags: bug, orm
        :tickets: 3349

        :class:`.Query` doesn't support joins, subselects, or special
        FROM clauses when using the :meth:`.Query.update` or
        :meth:`.Query.delete` methods; instead of silently ignoring these
        fields if methods like :meth:`.Query.join` or
        :meth:`.Query.select_from` has been called, a warning is emitted.
        As of 1.0.0b5 this will raise an error.

    .. change::
        :tags: bug, orm
        :tickets: 3352
        :versions: 1.0.0b5

        Fixed bug where the state tracking within multiple, nested
        :meth:`.Session.begin_nested` operations would fail to propagate
        the "dirty" flag for an object that had been updated within
        the inner savepoint, such that if the enclosing savepoint were
        rolled back, the object would not be part of the state that was
        expired and therefore reverted to its database state.

    .. change::
        :tags: bug, mysql, pymysql
        :tickets: 3337
        :versions: 1.0.0b4

        Fixed unicode support for PyMySQL when using an "executemany"
        operation with unicode parameters.  SQLAlchemy now passes both
        the statement as well as the bound parameters as unicode
        objects, as PyMySQL generally uses string interpolation
        internally to produce the final statement, and in the case of
        executemany does the "encode" step only on the final statement.

    .. change::
        :tags: bug, py3k, mysql
        :tickets: 3333
        :versions: 1.0.0b2

        Fixed the :class:`.mysql.BIT` type on Py3K which was not using the
        ``ord()`` function correctly.  Pull request courtesy David Marin.

    .. change::
        :tags: bug, ext
        :tickets: 3324

        Fixed regression from 0.9.9 where the :func:`.as_declarative`
        symbol was removed from the ``sqlalchemy.ext.declarative``
        namespace.

    .. change::
        :tags: feature, orm
        :tickets: 3320
        :versions: 1.0.0b1

        Added a new entry ``"entity"`` to the dictionaries returned by
        :attr:`.Query.column_descriptions`.  This refers to the primary ORM
        mapped class or aliased class that is referred to by the expression.
        Compared to the existing entry for ``"type"``, it will always be
        a mapped entity, even if extracted from a column expression, or
        None if the given expression is a pure core expression.
        See also :ticket:`3403` which repaired a regression in this feature
        which was unreleased in 0.9.10 but was released in the 1.0 version.


.. changelog::
    :version: 0.9.9
    :released: March 10, 2015

    .. change::
        :tags: feature, postgresql
        :versions: 1.0.0b1

        Added support for the ``CONCURRENTLY`` keyword with PostgreSQL
        indexes, established using ``postgresql_concurrently``.  Pull
        request courtesy Iuri de Silvio.

        .. seealso::

            :ref:`postgresql_index_concurrently`

    .. change::
        :tags: bug, ext, py3k
        :versions: 1.0.0b1

        Fixed bug where the association proxy list class would not interpret
        slices correctly under Py3K.  Pull request courtesy
        Gilles Dartiguelongue.

    .. change::
        :tags: feature, sqlite
        :versions: 1.0.0b1

        Added support for partial indexes (e.g. with a WHERE clause) on
        SQLite.  Pull request courtesy Kai Groner.

        .. seealso::

            :ref:`sqlite_partial_index`

    .. change::
        :tags: bug, orm
        :tickets: 3310
        :versions: 1.0.0b1

        Fixed bugs in ORM object comparisons where comparison of
        many-to-one ``!= None`` would fail if the source were an aliased
        class, or if the query needed to apply special aliasing to the
        expression due to aliased joins or polymorphic querying; also fixed
        bug in the case where comparing a many-to-one to an object state
        would fail if the query needed to apply special aliasing
        due to aliased joins or polymorphic querying.

    .. change::
        :tags: bug, orm
        :tickets: 3309
        :versions: 1.0.0b1

        Fixed bug where internal assertion would fail in the case where
        an ``after_rollback()`` handler for a :class:`.Session` incorrectly
        adds state to that :class:`.Session` within the handler, and the task
        to warn and remove this state (established by :ticket:`2389`) attempts
        to proceed.

    .. change::
        :tags: bug, orm
        :versions: 1.0.0b1

        Fixed bug where TypeError raised when :meth:`.Query.join` called
        with unknown kw arguments would raise its own TypeError due
        to broken formatting.  Pull request courtesy Malthe Borch.

    .. change::
        :tags: bug, engine
        :tickets: 3302
        :versions: 1.0.0b1

        Fixed bug in :class:`.Connection` and pool where the
        :meth:`.Connection.invalidate` method, or an invalidation due
        to a database disconnect, would fail if the
        ``isolation_level`` parameter had been used with
        :meth:`.Connection.execution_options`; the "finalizer" that resets
        the isolation level would be called on the no longer opened connection.

    .. change::
        :tags: feature, orm
        :tickets: 3296
        :versions: 1.0.0b1

        Added new parameter :paramref:`.Session.connection.execution_options`
        which may be used to set up execution options on a :class:`.Connection`
        when it is first checked out, before the transaction has begun.
        This is used to set up options such as isolation level on the
        connection before the transaction starts.

        .. seealso::

            :ref:`session_transaction_isolation` - new documentation section
            detailing best practices for setting transaction isolation with
            sessions.

    .. change::
        :tags: bug, engine
        :tickets: 3296
        :versions: 1.0.0b1

        A warning is emitted if the ``isolation_level`` parameter is used
        with :meth:`.Connection.execution_options` when a :class:`.Transaction`
        is in play; DBAPIs and/or SQLAlchemy dialects such as psycopg2,
        MySQLdb may implicitly rollback or commit the transaction, or
        not change the setting til next transaction, so this is never safe.

    .. change::
        :tags: bug, orm
        :tickets: 3300
        :versions: 1.0.0b1

        Fixed bug in lazy loading SQL construction whereby a complex
        primaryjoin that referred to the same "local" column multiple
        times in the "column that points to itself" style of self-referential
        join would not be substituted in all cases.   The logic to determine
        substitutions here has been reworked to be more open-ended.

    .. change::
        :tags: bug, postgresql
        :tickets: 2940
        :versions: 1.0.0b1

        Repaired support for PostgreSQL UUID types in conjunction with
        the ARRAY type when using psycopg2.  The psycopg2 dialect now
        employs use of the psycopg2.extras.register_uuid() hook
        so that UUID values are always passed to/from the DBAPI as
        UUID() objects.   The :paramref:`.UUID.as_uuid` flag is still
        honored, except with psycopg2 we need to convert returned
        UUID objects back into strings when this is disabled.

    .. change::
        :tags: bug, postgresql
        :versions: 1.0.0b1

        Added support for the :class:`postgresql.JSONB` datatype when
        using psycopg2 2.5.4 or greater, which features native conversion
        of JSONB data so that SQLAlchemy's converters must be disabled;
        additionally, the newly added psycopg2 extension
        ``extras.register_default_jsonb`` is used to establish a JSON
        deserializer passed to the dialect via the ``json_deserializer``
        argument.  Also repaired the PostgreSQL integration tests which
        weren't actually round-tripping the JSONB type as opposed to the
        JSON type.  Pull request courtesy Mateusz Susik.

    .. change::
        :tags: bug, postgresql
        :versions: 1.0.0b1

        Repaired the use of the "array_oid" flag when registering the
        HSTORE type with older psycopg2 versions < 2.4.3, which does not
        support this flag, as well as use of the native json serializer
        hook "register_default_json" with user-defined ``json_deserializer``
        on psycopg2 versions < 2.5, which does not include native json.

    .. change::
        :tags: bug, schema
        :tickets: 3298, 1765

        Fixed bug in 0.9's foreign key setup system, such that
        the logic used to link a :class:`.ForeignKey` to its parent could fail
        when the foreign key used "link_to_name=True" in conjunction with
        a target :class:`.Table` that would not receive its parent column until
        later, such as within a reflection + "useexisting" scenario,
        if the target column in fact had a key value different from its name,
        as would occur in reflection if column reflect events were used to
        alter the .key of reflected :class:`.Column` objects so that the
        link_to_name becomes significant.  Also repaired support for column
        type via FK transmission in a similar way when target columns had a
        different key and were referenced using link_to_name.

    .. change::
        :tags: feature, engine
        :versions: 1.0.0b1

        Added new user-space accessors for viewing transaction isolation
        levels; :meth:`.Connection.get_isolation_level`,
        :attr:`.Connection.default_isolation_level`.

    .. change::
        :tags: bug, postgresql
        :versions: 1.0.0b1
        :tickets: 3174

        Fixed bug where PostgreSQL dialect would fail to render an
        expression in an :class:`.Index` that did not correspond directly
        to a table-bound column; typically when a :func:`.text` construct
        was one of the expressions within the index; or could misinterpret the
        list of expressions if one or more of them were such an expression.

    .. change::
        :tags: bug, orm
        :versions: 1.0.0b1
        :tickets: 3287

        The "wildcard" loader options, in particular the one set up by
        the :func:`.orm.load_only` option to cover all attributes not
        explicitly mentioned, now takes into account the superclasses
        of a given entity, if that entity is mapped with inheritance mapping,
        so that attribute names within the superclasses are also omitted
        from the load.  Additionally, the polymorphic discriminator column
        is unconditionally included in the list, just in the same way that
        primary key columns are, so that even with load_only() set up,
        polymorphic loading of subtypes continues to function correctly.

    .. change::
        :tags: bug, sql
        :versions: 1.0.0b1

        Added the ``native_enum`` flag to the ``__repr__()`` output
        of :class:`.Enum`, which is mostly important when using it with
        Alembic autogenerate.  Pull request courtesy Dimitris Theodorou.

    .. change::
        :tags: bug, orm, pypy
        :versions: 1.0.0b1
        :tickets: 3285

        Fixed bug where if an exception were thrown at the start of a
        :class:`.Query` before it fetched results, particularly when
        row processors can't be formed, the cursor would stay open with
        results pending and not actually be closed.  This is typically only
        an issue on an interpreter like PyPy where the cursor isn't
        immediately GC'ed, and can in some circumstances lead to transactions/
        locks being open longer than is desirable.

    .. change::
        :tags: change, mysql
        :versions: 1.0.0b1
        :tickets: 3275

        The ``gaerdbms`` dialect is no longer necessary, and emits a
        deprecation warning.  Google now recommends using the MySQLdb
        dialect directly.

    .. change::
        :tags: bug, sql
        :versions: 1.0.0b1
        :tickets: 3278

        Fixed bug where using a :class:`.TypeDecorator` that implemented
        a type that was also a :class:`.TypeDecorator` would fail with
        Python's "Cannot create a consistent method resolution order (MRO)"
        error, when any kind of SQL comparison expression were used against
        an object using this type.

    .. change::
        :tags: bug, mysql
        :versions: 1.0.0b1
        :tickets: 3274

        Added a version check to the MySQLdb dialect surrounding the
        check for 'utf8_bin' collation, as this fails on MySQL server < 5.0.

    .. change::
        :tags: feature, orm
        :versions: 1.0.0b1

        Added new method :meth:`.Session.invalidate`, functions similarly
        to :meth:`.Session.close`, except also calls
        :meth:`.Connection.invalidate`
        on all connections, guaranteeing that they will not be returned to
        the connection pool.  This is useful in situations e.g. dealing
        with gevent timeouts when it is not safe to use the connection further,
        even for rollbacks.

    .. change::
        :tags: bug, examples
        :versions: 1.0.0b1

        Updated the :ref:`examples_versioned_history` example such that
        mapped columns are re-mapped to
        match column names as well as grouping of columns; in particular,
        this allows columns that are explicitly grouped in a same-column-named
        joined inheritance scenario to be mapped in the same way in the
        history mappings, avoiding warnings added in the 0.9 series
        regarding this pattern and allowing the same view of attribute
        keys.

    .. change::
        :tags: bug, examples
        :versions: 1.0.0b1

        Fixed a bug in the examples/generic_associations/discriminator_on_association.py
        example, where the subclasses of AddressAssociation were not being
        mapped as "single table inheritance", leading to problems when trying
        to use the mappings further.

    .. change::
        :tags: bug, orm
        :versions: 1.0.0b1
        :tickets: 3251

        Fixed a leak which would occur in the unsupported and highly
        non-recommended use case of replacing a relationship on a fixed
        mapped class many times, referring to an arbitrarily growing number of
        target mappers.  A warning is emitted when the old relationship is
        replaced, however if the mapping were already used for querying, the
        old relationship would still be referenced within some registries.

    .. change::
        :tags: bug, sql
        :versions: 1.0.0b1
        :tickets: 3248

        Fixed issue where the columns from a SELECT embedded in an
        INSERT, either through the values clause or as a "from select",
        would pollute the column types used in the result set produced by
        the RETURNING clause when columns from both statements shared the
        same name, leading to potential errors or mis-adaptation when
        retrieving the returning rows.

    .. change::
        :tags: bug, orm, sqlite
        :versions: 1.0.0b1
        :tickets: 3241

        Fixed bug regarding expression mutations which could express
        itself as a "Could not locate column" error when using
        :class:`.Query` to  select from multiple, anonymous column
        entities when querying against SQLite, as a side effect of the
        "join rewriting" feature used by the SQLite dialect.

    .. change::
        :tags: feature, sqlite
        :versions: 1.0.0b1

        Added a new SQLite backend for the SQLCipher backend.  This backend
        provides for encrypted SQLite databases using the pysqlcipher Python
        driver, which is very similar to the pysqlite driver.

        .. seealso::

            :mod:`~sqlalchemy.dialects.sqlite.pysqlcipher`

    .. change::
        :tags: bug, orm
        :tickets: 3232
        :versions: 1.0.0b1

        Fixed bug where the ON clause for :meth:`.Query.join`,
        and :meth:`.Query.outerjoin` to a single-inheritance subclass
        using ``of_type()`` would not render the "single table criteria" in
        the ON clause if the ``from_joinpoint=True`` flag were set.

.. changelog::
    :version: 0.9.8
    :released: October 13, 2014

    .. change::
        :tags: bug, mysql, mysqlconnector
        :versions: 1.0.0b1

        Mysqlconnector as of version 2.0, probably as a side effect of
        the  python 3 merge, now does not expect percent signs (e.g.
        as used as the modulus operator and others) to be doubled,
        even when using the "pyformat" bound parameter format (this
        change is not documented by Mysqlconnector).  The dialect now
        checks for py2k and for mysqlconnector less than version 2.0
        when detecting if the modulus operator should be rendered as
        ``%%`` or ``%``.

    .. change::
        :tags: bug, mysql, mysqlconnector
        :versions: 1.0.0b1

        Unicode SQL is now passed for MySQLconnector version 2.0 and above;
        for Py2k and MySQL < 2.0, strings are encoded.


    .. change::
        :tags: bug, oracle
        :versions: 1.0.0b1
        :tickets: 2138

        Fixed long-standing bug in Oracle dialect where bound parameter
        names that started with numbers would not be quoted, as Oracle
        doesn't like numerics in bound parameter names.

    .. change::
        :tags: bug, sql
        :versions: 1.0.0b1
        :tickets: 3195

        Fixed bug where a fair number of SQL elements within
        the sql package would fail to ``__repr__()`` successfully,
        due to a missing ``description`` attribute that would then invoke
        a recursion overflow when an internal AttributeError would then
        re-invoke ``__repr__()``.

    .. change::
        :tags: bug, declarative, orm
        :versions: 1.0.0b1
        :tickets: 3185

        Fixed "'NoneType' object has no attribute 'concrete'" error
        when using :class:`.AbstractConcreteBase` in conjunction with
        a subclass that declares ``__abstract__``.

    .. change::
        :tags: bug, engine
        :versions: 1.0.0b1
        :tickets: 3200

        The execution options passed to an :class:`.Engine` either via
        :paramref:`.create_engine.execution_options` or
        :meth:`.Engine.update_execution_options` are not passed to the
        special :class:`.Connection` used to initialize the dialect
        within the "first connect" event; dialects will usually
        perform their own queries in this phase, and none of the
        current available  options should be applied here.  In
        particular, the "autocommit" option was causing an attempt to
        autocommit within this initial connect which would fail with
        an AttributeError due to the non-standard state of the
        :class:`.Connection`.

    .. change::
        :tags: bug, sqlite
        :versions: 1.0.0b1
        :tickets: 3211

        When selecting from a UNION using an attached database file,
        the pysqlite driver reports column names in cursor.description
        as 'dbname.tablename.colname', instead of 'tablename.colname' as
        it normally does for a UNION (note that it's supposed to just be
        'colname' for both, but we work around it).  The column translation
        logic here has been adjusted to retrieve the rightmost token, rather
        than the second token, so it works in both cases.   Workaround
        courtesy Tony Roberts.

    .. change::
        :tags: bug, postgresql
        :versions: 1.0.0b1
        :tickets: 3021

        A revisit to this issue first patched in 0.9.5, apparently
        psycopg2's ``.closed`` accessor is not as reliable as we assumed,
        so we have added an explicit check for the exception messages
        "SSL SYSCALL error: Bad file descriptor" and
        "SSL SYSCALL error: EOF detected" when detecting an
        is-disconnect scenario.   We will continue to consult psycopg2's
        connection.closed as a first check.

    .. change::
        :tags: bug, orm, engine
        :versions: 1.0.0b1
        :tickets: 3197

        Fixed bug that affected generally the same classes of event
        as that of :ticket:`3199`, when the ``named=True`` parameter
        would be used.  Some events would fail to register, and others
        would not invoke the event arguments correctly, generally in the
        case of when an event was "wrapped" for adaption in some other way.
        The "named" mechanics have been rearranged to not interfere with
        the argument signature expected by internal wrapper functions.

    .. change::
        :tags: bug, declarative
        :versions: 1.0.0b1
        :tickets: 3208

        Fixed an unlikely race condition observed in some exotic end-user
        setups, where the attempt to check for "duplicate class name" in
        declarative would hit upon a not-totally-cleaned-up weak reference
        related to some other class being removed; the check here now ensures
        the weakref still references an object before calling upon it further.

    .. change::
        :tags: bug, orm
        :versions: 1.0.0b1
        :tickets: 3199

        Fixed bug that affected many classes of event, particularly
        ORM events but also engine events, where the usual logic of
        "de duplicating" a redundant call to :func:`.event.listen`
        with the same arguments would fail, for those events where the
        listener function is wrapped.  An assertion would be hit within
        registry.py.  This assertion has now been integrated into the
        deduplication check, with the added bonus of a simpler means
        of checking deduplication across the board.

    .. change::
        :tags: bug, mssql
        :versions: 1.0.0b1
        :tickets: 3151

        Fixed the version string detection in the pymssql dialect to
        work with Microsoft SQL Azure, which changes the word "SQL Server"
        to "SQL Azure".

    .. change::
        :tags: bug, orm
        :versions: 1.0.0b1
        :tickets: 3194

        Fixed warning that would emit when a complex self-referential
        primaryjoin contained functions, while at the same time remote_side
        was specified; the warning would suggest setting "remote side".
        It now only emits if remote_side isn't present.

    .. change::
        :tags: bug, ext
        :versions: 1.0.0b1
        :tickets: 3191

        Fixed bug in ordering list where the order of items would be
        thrown off during a collection replace event, if the
        reorder_on_append flag were set to True.  The fix ensures that the
        ordering list only impacts the list that is explicitly associated
        with the object.

    .. change::
        :tags: bug, sql
        :versions: 1.0.0b1
        :tickets: 3180

        An adjustment to table/index reflection such that if an index
        reports a column that isn't found to be present in the table,
        a warning is emitted and the column is skipped.  This can occur
        for some special system column situations as has been observed
        with Oracle.

    .. change::
        :tags: bug, ext
        :versions: 1.0.0b1

        Fixed bug where :class:`.ext.mutable.MutableDict`
        failed to implement the ``update()`` dictionary method, thus
        not catching changes. Pull request courtesy Matt Chisholm.

    .. change::
        :tags: bug, ext
        :versions: 1.0.0b1

        Fixed bug where a custom subclass of :class:`.ext.mutable.MutableDict`
        would not show up in a "coerce" operation, and would instead
        return a plain :class:`.ext.mutable.MutableDict`.  Pull request
        courtesy Matt Chisholm.

    .. change::
        :tags: bug, pool
        :versions: 1.0.0b1
        :tickets: 3168

        Fixed bug in connection pool logging where the "connection checked out"
        debug logging message would not emit if the logging were set up using
        ``logging.setLevel()``, rather than using the ``echo_pool`` flag.
        Tests to assert this logging have been added.  This is a
        regression that was introduced in 0.9.0.

    .. change::
        :tags: feature, postgresql, pg8000
        :versions: 1.0.0b1

        Support is added for "sane multi row count" with the pg8000 driver,
        which applies mostly to when using versioning with the ORM.
        The feature is version-detected based on pg8000 1.9.14 or greater
        in use.  Pull request courtesy Tony Locke.

    .. change::
        :tags: bug, engine
        :versions: 1.0.0b1
        :tickets: 3165

        The string keys that are used to determine the columns impacted
        for an INSERT or UPDATE are now sorted when they contribute towards
        the "compiled cache" cache key.   These keys were previously not
        deterministically ordered, meaning the same statement could be
        cached multiple times on equivalent keys, costing both in terms of
        memory as well as performance.

    .. change::
        :tags: bug, postgresql
        :versions: 1.0.0b1
        :tickets: 3159

        Fixed bug where PostgreSQL JSON type was not able to persist or
        otherwise render a SQL NULL column value, rather than a JSON-encoded
        ``'null'``.  To support this case, changes are as follows:

        * The value :func:`.null` can now be specified, which will always
          result in a NULL value resulting in the statement.

        * A new parameter :paramref:`.JSON.none_as_null` is added, which
          when True indicates that the Python ``None`` value should be
          persisted as SQL NULL, rather than JSON-encoded ``'null'``.

        Retrival of NULL as None is also repaired for DBAPIs other than
        psycopg2, namely pg8000.

    .. change::
        :tags: bug, sql
        :versions: 1.0.0b1
        :tickets: 3154

        Fixed bug in CTE where ``literal_binds`` compiler argument would not
        be always be correctly propagated when one CTE referred to another
        aliased CTE in a statement.

    .. change::
        :tags: bug, postgresql
        :versions: 1.0.0b1
        :tickets: 3075

        The exception wrapping system for DBAPI errors can now accommodate
        non-standard DBAPI exceptions, such as the psycopg2
        TransactionRollbackError.  These exceptions will now be raised
        using the closest available subclass in ``sqlalchemy.exc``, in the
        case of TransactionRollbackError, ``sqlalchemy.exc.OperationalError``.

    .. change::
        :tags: bug, sql
        :versions: 1.0.0b1
        :tickets: 3144, 3067

        Fixed 0.9.7 regression caused by :ticket:`3067` in conjunction with
        a mis-named unit test such that so-called "schema" types like
        :class:`.Boolean` and :class:`.Enum` could no longer be pickled.

    .. change::
        :tags: bug, postgresql
        :versions: 1.0.0b1
        :tickets: 3141

        Fixed bug in :class:`.postgresql.array` object where comparison
        to a plain Python list would fail to use the correct array constructor.
        Pull request courtesy Andrew.

    .. change::
        :tags: bug, postgresql
        :versions: 1.0.0b1
        :tickets: 3137

        Added a supported :meth:`.FunctionElement.alias` method to functions,
        e.g. the ``func`` construct.  Previously, behavior for this method
        was undefined.  The current behavior mimics that of pre-0.9.4,
        which is that the function is turned into a single-column FROM
        clause with the given alias name, where the column itself is
        anonymously named.

.. changelog::
    :version: 0.9.7
    :released: July 22, 2014

    .. change::
        :tags: bug, postgresql, pg8000
        :tickets: 3134
        :versions: 1.0.0b1

        Fixed bug introduced in 0.9.5 by new pg8000 isolation level feature
        where engine-level isolation level parameter would raise an error
        on connect.

    .. change::
        :tags: bug, oracle, tests
        :tickets: 3128
        :versions: 1.0.0b1

        Fixed bug in oracle dialect test suite where in one test,
        'username' was assumed to be in the database URL, even though
        this might not be the case.

    .. change::
        :tags: bug, orm, eagerloading
        :tickets: 3131
        :versions: 1.0.0b1

        Fixed a regression caused by :ticket:`2976` released in 0.9.4 where
        the "outer join" propagation along a chain of joined eager loads
        would incorrectly convert an "inner join" along a sibling join path
        into an outer join as well, when only descendant paths should be
        receiving the "outer join" propagation; additionally, fixed related
        issue where "nested" join propagation would take place inappropriately
        between two sibling join paths.

    .. change::
        :tags: bug, sqlite
        :tickets: 3130
        :versions: 1.0.0b1

        Fixed a SQLite join rewriting issue where a subquery that is embedded
        as a scalar subquery such as within an IN would receive inappropriate
        substitutions from the enclosing query, if the same table were present
        inside the subquery as were in the enclosing query such as in a
        joined inheritance scenario.

    .. change::
        :tags: bug, sql
        :tickets: 3067
        :versions: 1.0.0b1

        Fix bug in naming convention feature where using a check
        constraint convention that includes ``constraint_name`` would
        then force all :class:`.Boolean` and :class:`.Enum` types to
        require names as well, as these implicitly create a
        constraint, even if the ultimate target backend were one that does
        not require generation of the constraint such as PostgreSQL.
        The mechanics of naming conventions for these particular
        constraints has been reorganized such that the naming
        determination is done at DDL compile time, rather than at
        constraint/table construction time.

    .. change::
        :tags: bug, mssql
        :tickets: 3025

        Fixed a regression from 0.9.5 caused by :ticket:`3025` where the
        query used to determine "default schema" is invalid in SQL Server 2000.
        For SQL Server 2000 we go back to defaulting to the "schema name"
        parameter of the dialect, which is configurable but defaults
        to 'dbo'.

    .. change::
        :tags: bug, orm
        :tickets: 3083, 2736
        :versions: 1.0.0b1

        Fixed a regression from 0.9.0 due to :ticket:`2736` where the
        :meth:`.Query.select_from` method no longer set up the "from
        entity" of the :class:`.Query` object correctly, so that
        subsequent :meth:`.Query.filter_by` or :meth:`.Query.join`
        calls would fail to check the appropriate "from" entity when
        searching for attributes by string name.

    .. change::
        :tags: bug, sql
        :tickets: 3090
        :versions: 1.0.0b1

        Fixed bug in common table expressions whereby positional bound
        parameters could be expressed in the wrong final order
        when CTEs were nested in certain ways.

    .. change::
        :tags: bug, sql
        :tickets: 3069
        :versions: 1.0.0b1

        Fixed bug where multi-valued :class:`.Insert` construct would fail
        to check subsequent values entries beyond the first one given
        for literal SQL expressions.

    .. change::
        :tags: bug, sql
        :tickets: 3123
        :versions: 1.0.0b1

        Added a "str()" step to the dialect_kwargs iteration for
        Python version < 2.6.5, working around the
        "no unicode keyword arg" bug as these args are passed along as
        keyword args within some reflection processes.

    .. change::
        :tags: bug, sql
        :tickets: 3122
        :versions: 1.0.0b1

        The :meth:`.TypeEngine.with_variant` method will now accept a
        type class as an argument which is internally converted to an
        instance, using the same convention long established by other
        constructs such as :class:`.Column`.

    .. change::
        :tags: bug, orm
        :tickets: 3117

        The "evaluator" for query.update()/delete() won't work with multi-table
        updates, and needs to be set to `synchronize_session=False` or
        `synchronize_session='fetch'`; a warning is now emitted.  In
        1.0 this will be promoted to a full exception.

    .. change::
        :tags: bug, tests
        :versions: 1.0.0b1

        Fixed bug where "python setup.py test" wasn't calling into
        distutils appropriately, and errors would be emitted at the end
        of the test suite.

    .. change::
        :tags: feature, postgresql
        :versions: 1.0.0b1
        :tickets: 3078

        Added kw argument ``postgresql_regconfig`` to the
        :meth:`.ColumnOperators.match` operator, allows the "reg config" argument
        to be specified to the ``to_tsquery()`` function emitted.
        Pull request courtesy Jonathan Vanasco.

    .. change::
        :tags: feature, postgresql
        :versions: 1.0.0b1

        Added support for PostgreSQL JSONB via :class:`.JSONB`.  Pull request
        courtesy Damian Dimmich.

    .. change::
        :tags: feature, mssql
        :versions: 1.0.0b1

        Enabled "multivalues insert" for SQL Server 2008.  Pull request
        courtesy Albert Cervin.  Also expanded the checks for "IDENTITY INSERT"
        mode to include when the identity key is present in the
        VALUEs clause of the statement.

    .. change::
        :tags: feature, engine
        :tickets: 3076
        :versions: 1.0.0b1

        Added new event :meth:`.ConnectionEvents.handle_error`, a more
        fully featured and comprehensive replacement for
        :meth:`.ConnectionEvents.dbapi_error`.

    .. change::
        :tags: bug, orm
        :tickets: 3108
        :versions: 1.0.0b1

        Fixed bug where items that were persisted, deleted, or had a
        primary key change within a savepoint block would not
        participate in being restored to their former state (not in
        session, in session, previous PK) after the outer transaction
        were rolled back.

    .. change::
        :tags: bug, orm
        :tickets: 3106
        :versions: 1.0.0b1

        Fixed bug in subquery eager loading in conjunction with
        :func:`.with_polymorphic`, the targeting of entities and columns
        in the subquery load has been made more accurate with respect
        to this type of entity and others.

    .. change::
        :tags: bug, orm
        :tickets: 3099

        Fixed bug involving dynamic attributes, that was again a regression
        of :ticket:`3060` from version 0.9.5.  A self-referential relationship
        with lazy='dynamic' would raise a TypeError within a flush operation.

    .. change::
        :tags: bug, declarative
        :tickets: 3097
        :versions: 1.0.0b1

        Fixed bug when the declarative ``__abstract__`` flag was not being
        distinguished for when it was actually the value ``False``.
        The ``__abstract__`` flag needs to actually evaluate to a True
        value at the level being tested.

.. changelog::
    :version: 0.9.6
    :released: June 23, 2014

    .. change::
        :tags: bug, orm
        :tickets: 3060

        Reverted the change for :ticket:`3060` - this is a unit of work
        fix that is updated more comprehensively in 1.0 via :ticket:`3061`.
        The fix in :ticket:`3060` unfortunately produces a new issue whereby
        an eager load of a many-to-one attribute can produce an event
        that is interpreted into an attribute change.

.. changelog::
    :version: 0.9.5
    :released: June 23, 2014

    .. change::
        :tags: bug, orm
        :tickets: 3042
        :versions: 1.0.0b1

        Additional checks have been added for the case where an inheriting
        mapper is implicitly combining one of its column-based attributes
        with that of the parent, where those columns normally don't necessarily
        share the same value.  This is an extension of an existing check that
        was added via :ticket:`1892`; however this new check emits only a
        warning, instead of an exception, to allow for applications that may
        be relying upon the existing behavior.

        .. seealso::

            :ref:`faq_combining_columns`

    .. change::
        :tags: bug, sql
        :tickets: 3023
        :versions: 1.0.0b1

        The :paramref:`.Column.nullable` flag is implicitly set to ``False``
        when that :class:`.Column` is referred to in an explicit
        :class:`.PrimaryKeyConstraint` for that table.  This behavior now
        matches that of when the :class:`.Column` itself has the
        :paramref:`.Column.primary_key` flag set to ``True``, which is
        intended to be an exactly equivalent case.

    .. change::
        :tags: enhancement, postgresql
        :tickets: 3002
        :versions: 1.0.0b1

        Added a new type :class:`.postgresql.OID` to the PostgreSQL dialect.
        While "oid" is generally a private type within PG that is not exposed
        in modern versions, there are some PG use cases such as large object
        support where these types might be exposed, as well as within some
        user-reported schema reflection use cases.

    .. change::
        :tags: bug, orm
        :tickets: 3080
        :versions: 1.0.0b1

        Modified the behavior of :func:`.orm.load_only` such that primary key
        columns are always added to the list of columns to be "undeferred";
        otherwise, the ORM can't load the row's identity.   Apparently,
        one can defer the mapped primary keys and the ORM will fail, that
        hasn't been changed.  But as load_only is essentially saying
        "defer all but X", it's more critical that PK cols not be part of this
        deferral.

    .. change::
        :tags: feature, examples
        :versions: 1.0.0b1

        Added a new example illustrating materialized paths, using the
        latest relationship features.   Example courtesy Jack Zhou.

    .. change::
        :tags: bug, testsuite
        :versions: 1.0.0b1

        In public test suite, changed to use of ``String(40)`` from
        less-supported ``Text`` in ``StringTest.test_literal_backslashes``.
        Pullreq courtesy Jan.

    .. change::
        :tags: bug, engine
        :versions: 1.0.0b1
        :tickets: 3063

        Fixed bug which would occur if a DBAPI exception
        occurs when the engine first connects and does its initial checks,
        and the exception is not a disconnect exception, yet the cursor
        raises an error when we try to close it.  In this case the real
        exception would be quashed as we tried to log the cursor close
        exception via the connection pool and failed, as we were trying
        to access the pool's logger in a way that is inappropriate
        in this very specific scenario.

    .. change::
        :tags: feature, postgresql
        :versions: 1.0.0b1

        Added support for AUTOCOMMIT isolation level when using the pg8000
        DBAPI.  Pull request courtesy Tony Locke.

    .. change::
        :tags: bug, postgresql
        :tickets: 3021
        :versions: 1.0.0b1

        The psycopg2 ``.closed`` accessor is now consulted when determining
        if an exception is a "disconnect" error; ideally, this should remove
        the need for any other inspection of the exception message to detect
        disconnect, however we will leave those existing messages in place
        as a fallback.   This should be able to handle newer cases like
        "SSL EOF" conditions.  Pull request courtesy Dirk Mueller.

    .. change::
        :tags: bug, orm
        :tickets: 3060
        :versions: 1.0.0b1

        Fixed a few edge cases which arise in the so-called "row switch"
        scenario, where an INSERT/DELETE can be turned into an UPDATE.
        In this situation, a many-to-one relationship set to None, or
        in some cases a scalar attribute set to None, may not be detected
        as a net change in value, and therefore the UPDATE would not reset
        what was on the previous row.   This is due to some as-yet
        unresolved side effects of the way attribute history works in terms
        of implicitly assuming None isn't really a "change" for a previously
        un-set attribute.  See also :ticket:`3061`.

        .. note::

            This change has been **REVERTED** in 0.9.6.   The full fix
            will be in version 1.0 of SQLAlchemy.


    .. change::
        :tags: bug, orm
        :versions: 1.0.0b1

        Related to :ticket:`3060`, an adjustment has been made to the unit
        of work such that loading for related many-to-one objects is slightly
        more aggressive, in the case of a graph of self-referential objects
        that are to be deleted; the load of related objects is to help
        determine the correct order for deletion if passive_deletes is
        not set.

    .. change::
        :tags: bug, orm
        :tickets: 3057
        :versions: 1.0.0b1

        Fixed bug in SQLite join rewriting where anonymized column names
        due to repeats would not correctly be rewritten in subqueries.
        This would affect SELECT queries with any kind of subquery + join.

    .. change::
        :tags: bug, sql
        :tickets: 3012
        :versions: 1.0.0b1

        Fixed bug where the :meth:`.Operators.__and__`,
        :meth:`.Operators.__or__` and :meth:`.Operators.__invert__`
        operator overload methods could not be overridden within a custom
        :class:`.TypeEngine.Comparator` implementation.

    .. change::
        :tags: feature, postgresql
        :tickets: 2785
        :versions: 1.0.0b1

        Added a new flag :paramref:`.ARRAY.zero_indexes` to the PostgreSQL
        :class:`.ARRAY` type.  When set to ``True``, a value of one will be
        added to all array index values before passing to the database, allowing
        better interoperability between Python style zero-based indexes and
        PostgreSQL one-based indexes.  Pull request courtesy Alexey Terentev.

    .. change::
        :tags: bug, engine
        :tickets: 3043
        :versions: 1.0.0b1

        Fixed some "double invalidate" situations were detected where
        a connection invalidation could occur within an already critical section
        like a connection.close(); ultimately, these conditions are caused
        by the change in :ticket:`2907`, in that the "reset on return" feature
        calls out to the Connection/Transaction in order to handle it, where
        "disconnect detection" might be caught.  However, it's possible that
        the more recent change in :ticket:`2985` made it more likely for this
        to be seen as the "connection invalidate" operation is much quicker,
        as the issue is more reproducible on 0.9.4 than 0.9.3.

        Checks are now added within any section that
        an invalidate might occur to halt further disallowed operations
        on the invalidated connection.  This includes two fixes both at the
        engine level and at the pool level.   While the issue was observed
        with highly concurrent gevent cases, it could in theory occur in
        any kind of scenario where a disconnect occurs within the connection
        close operation.

    .. change::
        :tags: feature, orm
        :tickets: 3029
        :versions: 1.0.0b1

        The "primaryjoin" model has been stretched a bit further to allow
        a join condition that is strictly from a single column to itself,
        translated through some kind of SQL function or expression.  This
        is kind of experimental, but the first proof of concept is a
        "materialized path" join condition where a path string is compared
        to itself using "like".   The :meth:`.ColumnOperators.like` operator has
        also been added to the list of valid operators to use in a primaryjoin
        condition.

    .. change::
        :tags: feature, sql
        :tickets: 3028
        :versions: 1.0.0b1

        Liberalized the contract for :class:`.Index` a bit in that you can
        specify a :func:`.text` expression as the target; the index no longer
        needs to have a table-bound column present if the index is to be
        manually added to the table, either via inline declaration or via
        :meth:`.Table.append_constraint`.

    .. change::
        :tags: bug, firebird
        :tickets: 3038

        Fixed bug where the combination of "limit" rendering as
        "SELECT FIRST n ROWS" using a bound parameter (only firebird has both),
        combined with column-level subqueries
        which also feature "limit" as well as "positional" bound parameters
        (e.g. qmark style) would erroneously assign the subquery-level positions
        before that of the enclosing SELECT, thus returning parameters which
        are out of order.

    .. change::
        :tags: bug, mssql
        :tickets: 3025
        :versions: 1.0.0b1

        Revised the query used to determine the current default schema name
        to use the ``database_principal_id()`` function in conjunction with
        the ``sys.database_principals`` view so that we can determine
        the default schema independently of the type of login in progress
        (e.g., SQL Server, Windows, etc).

    .. change::
        :tags: bug, sql
        :tickets: 3024
        :versions: 1.0.0b1

        Fixed bug in new :meth:`.DialectKWArgs.argument_for` method where
        adding an argument for a construct not previously included for any
        special arguments would fail.

    .. change::
        :tags: bug, py3k, tests
        :tickets: 2830
        :versions: 1.0.0b1

        Corrected for some deprecation warnings involving the ``imp``
        module and Python 3.3 or greater, when running tests.  Pull
        request courtesy Matt Chisholm.

    .. change::
        :tags: bug, sql
        :tickets: 3020, 1068
        :versions: 1.0.0b1

        Fixed regression introduced in 0.9 where new "ORDER BY <labelname>"
        feature from :ticket:`1068` would not apply quoting rules to the
        label name as rendered in the ORDER BY.

    .. change::
        :tags: feature, orm
        :tickets: 3017
        :versions: 1.0.0b1

        Added new utility function :func:`.make_transient_to_detached` which can
        be used to manufacture objects that behave as though they were loaded
        from a session, then detached.   Attributes that aren't present
        are marked as expired, and the object can be added to a Session
        where it will act like a persistent one.

    .. change::
        :tags: bug, sql
        :versions: 1.0.0b1

        Restored the import for :class:`.Function` to the ``sqlalchemy.sql.expression``
        import namespace, which was removed at the beginning of 0.9.

    .. change::
        :tags: bug, orm, sql
        :tickets: 3013
        :versions: 1.0.0b1

        Fixes to the newly enhanced boolean coercion in :ticket:`2804` where
        the new rules for "where" and "having" woudn't take effect for the
        "whereclause" and "having" kw arguments of the :func:`.select` construct,
        which is also what :class:`.Query` uses so wasn't working in the
        ORM either.

    .. change::
        :tags: feature, sql
        :tickets: 2990
        :versions: 1.0.0b1

        Added new flag :paramref:`.expression.between.symmetric`, when set to True
        renders "BETWEEN SYMMETRIC".  Also added a new negation operator
        "notbetween_op", which now allows an expression like ``~col.between(x, y)``
        to render as "col NOT BETWEEN x AND y", rather than a parenthesized NOT
        string.

.. changelog::
    :version: 0.9.4
    :released: March 28, 2014

    .. change::
        :tags: feature, orm
        :tickets: 3007

        Added new parameter :paramref:`.orm.mapper.confirm_deleted_rows`.  Defaults
        to True, indicates that a series of DELETE statements should confirm
        that the cursor rowcount matches the number of primary keys that should
        have matched;  this behavior had been taken off in most cases
        (except when version_id is used) to support the unusual edge case of
        self-referential ON DELETE CASCADE; to accommodate this, the message
        is now just a warning, not an exception, and the flag can be used
        to indicate a mapping that expects self-referential cascaded
        deletes of this nature.  See also :ticket:`2403` for background on the
        original change.

    .. change::
        :tags: bug, ext, automap
        :tickets: 3004

        Added support to automap for the case where a relationship should
        not be created between two classes that are in a joined inheritance
        relationship, for those foreign keys that link the subclass back to
        the superclass.

    .. change::
        :tags: bug, orm
        :tickets: 2948

        Fixed a very old behavior where the lazy load emitted for a one-to-many
        could inappropriately pull in the parent table, and also return results
        inconsistent based on what's in the parent table, when the primaryjoin
        includes some kind of discriminator against the parent table, such
        as ``and_(parent.id == child.parent_id, parent.deleted == False)``.
        While this primaryjoin doesn't make that much sense for a one-to-many,
        it is slightly more common when applied to the many-to-one side, and
        the one-to-many comes as a result of a backref.
        Loading rows from ``child`` in this case would keep ``parent.deleted == False``
        as is within the query, thereby yanking it into the FROM clause
        and doing a cartesian product.  The new behavior will now substitute
        the value of the local "parent.deleted" for that parameter as is
        appropriate.   Though typically, a real-world app probably wants to use a
        different primaryjoin for the o2m side in any case.

    .. change::
        :tags: bug, orm
        :tickets: 2965

        Improved the check for "how to join from A to B" such that when
        a table has multiple, composite foreign keys targeting a parent table,
        the :paramref:`.relationship.foreign_keys` argument will be properly
        interpreted in order to resolve the ambiguity; previously this condition
        would raise that there were multiple FK paths when in fact the
        foreign_keys argument should be establishing which one is expected.

    .. change::
        :tags: bug, mysql

        Tweaked the settings for mysql-connector-python; in Py2K, the
        "supports unicode statements" flag is now False, so that SQLAlchemy
        will encode the *SQL string* (note: *not* the parameters)
        to bytes before sending to the database.  This seems to allow
        all unicode-related tests to pass for mysql-connector, including those
        that use non-ascii table/column names, as well as some tests for the
        TEXT type using unicode under cursor.executemany().

    .. change::
        :tags: feature, engine

        Added some new event mechanics for dialect-level events; the initial
        implementation allows an event handler to redefine the specific mechanics
        by which an arbitrary dialect invokes execute() or executemany() on a
        DBAPI cursor.  The new events, at this point semi-public and experimental,
        are in support of some upcoming transaction-related extensions.

    .. change::
        :tags: feature, engine
        :tickets: 2978

        An event listener can now be associated with a :class:`.Engine`,
        after one or more :class:`.Connection` objects have been created
        (such as by an orm :class:`.Session` or via explicit connect)
        and the listener will pick up events from those connections.
        Previously, performance concerns pushed the event transfer from
        :class:`.Engine` to  :class:`.Connection` at init-time only, but
        we've inlined a bunch of conditional checks to make this possible
        without any additional function calls.

    .. change::
        :tags: bug, tests
        :tickets: 2980

        Fixed a few errant ``u''`` strings that would prevent tests from passing
        in Py3.2.  Patch courtesy Arfrever Frehtes Taifersar Arahesis.

    .. change::
        :tags: bug, engine
        :tickets: 2985

        A major improvement made to the mechanics by which the :class:`.Engine`
        recycles the connection pool when a "disconnect" condition is detected;
        instead of discarding the pool and explicitly closing out connections,
        the pool is retained and a "generational" timestamp is updated to
        reflect the current time, thereby causing all existing connections
        to be recycled when they are next checked out.   This greatly simplifies
        the recycle process, removes the need for "waking up" connect attempts
        waiting on the old pool and eliminates the race condition that many
        immediately-discarded "pool" objects could be created during the
        recycle operation.

    .. change::
        :tags: bug, oracle
        :tickets: 2987

        Added new datatype :class:`.oracle.DATE`, which is a subclass of
        :class:`.DateTime`.  As Oracle has no "datetime" type per se,
        it instead has only ``DATE``, it is appropriate here that the
        ``DATE`` type as present in the Oracle dialect be an instance of
        :class:`.DateTime`.  This issue doesn't change anything as far as
        the behavior of the type, as data conversion is handled by the
        DBAPI in any case, however the improved subclass layout will help
        the use cases of inspecting types for cross-database compatibility.
        Also removed uppercase ``DATETIME`` from the Oracle dialect as this
        type isn't functional in that context.

    .. change::
        :tags: bug, sql
        :tickets: 2988

        Fixed an 0.9 regression where a :class:`.Table` that failed to
        reflect correctly wouldn't be removed from the parent
        :class:`.MetaData`, even though in an invalid state.  Pullreq
        courtesy Roman Podoliaka.

    .. change::
        :tags: bug, engine

        The :meth:`.ConnectionEvents.after_cursor_execute` event is now
        emitted for the "_cursor_execute()" method of :class:`.Connection`;
        this is the "quick" executor that is used for things like
        when a sequence is executed ahead of an INSERT statement, as well as
        for dialect startup checks like unicode returns, charset, etc.
        the :meth:`.ConnectionEvents.before_cursor_execute` event was already
        invoked here.  The "executemany" flag is now always set to False
        here, as this event always corresponds to a single execution.
        Previously the flag could be True if we were acting on behalf of
        an executemany INSERT statement.

    .. change::
        :tags: bug, orm

        Added support for the not-quite-yet-documented ``insert=True``
        flag for :func:`.event.listen` to work with mapper / instance events.

    .. change::
        :tags: feature, sql

        Added support for literal rendering of boolean values, e.g.
        "true" / "false" or "1" / "0".

    .. change::
        :tags: feature, sql

        Added a new feature :func:`.schema.conv`, the purpose of which is to
        mark a constraint name as already having had a naming convention applied.
        This token will be used by Alembic migrations as of Alembic 0.6.4
        in order to render constraints in migration scripts with names marked
        as already having been subject to a naming convention.

    .. change::
        :tags: bug, sql

        :paramref:`.MetaData.naming_convention` feature will now also
        apply to :class:`.CheckConstraint` objects that are associated
        directly with a :class:`.Column` instead of just on the
        :class:`.Table`.

    .. change::
        :tags: bug, sql
        :tickets: 2991

        Fixed bug in new :paramref:`.MetaData.naming_convention` feature
        where the name of a check constraint making use of the
        `"%(constraint_name)s"` token would get doubled up for the
        constraint generated by a boolean or enum type, and overall
        duplicate events would cause the `"%(constraint_name)s"` token
        to keep compounding itself.

    .. change::
        :tags: feature, orm

        A warning is emitted if the :meth:`.MapperEvents.before_configured`
        or :meth:`.MapperEvents.after_configured` events are applied to a
        specific mapper or mapped class, as the events are only invoked
        for the :class:`.Mapper` target at the general level.

    .. change::
        :tags: feature, orm

        Added a new keyword argument ``once=True`` to :func:`.event.listen`
        and :func:`.event.listens_for`.  This is a convenience feature which
        will wrap the given listener such that it is only invoked once.

    .. change::
        :tags: feature, oracle
        :tickets: 2911

        Added a new engine option ``coerce_to_unicode=True`` to the
        cx_Oracle dialect, which restores the cx_Oracle outputtypehandler
        approach to Python unicode conversion under Python 2, which was
        removed in 0.9.2 as a result of :ticket:`2911`.  Some use cases would
        prefer that unicode coercion is unconditional for all string values,
        despite performance concerns.  Pull request courtesy
        Christoph Zwerschke.

    .. change::
        :tags: bug, pool

        Fixed small issue in :class:`.SingletonThreadPool` where the current
        connection to be returned might get inadvertently cleaned out during
        the "cleanup" process.  Patch courtesy jd23.

    .. change::
        :tags: bug, ext, py3k

        Fixed bug in association proxy where assigning an empty slice
        (e.g. ``x[:] = [...]``) would fail on Py3k.

    .. change::
        :tags: bug, general
        :tickets: 2979

        Fixed some test/feature failures occurring in Python 3.4,
        in particular the logic used to wrap "column default" callables
        wouldn't work properly for Python built-ins.

    .. change::
        :tags: feature, general

        Support has been added for pytest to run tests.   This runner
        is currently being supported in addition to nose, and will likely
        be preferred to nose going forward.   The nose plugin system used
        by SQLAlchemy has been split out so that it works under pytest as
        well.  There are no plans to drop support for nose at the moment
        and we hope that the test suite itself can continue to remain as
        agnostic of testing platform as possible.  See the file
        README.unittests.rst for updated information on running tests
        with pytest.

        The test plugin system has also been enhanced to support running
        tests against multiple database URLs at once, by specifying the ``--db``
        and/or ``--dburi`` flags multiple times.  This does not run the entire test
        suite for each database, but instead allows test cases that are specific
        to certain backends make use of that backend as the test is run.
        When using pytest as the test runner, the system will also run
        specific test suites multiple times, once for each database, particularly
        those tests within the "dialect suite".   The plan is that the enhanced
        system will also be used by Alembic, and allow Alembic to run
        migration operation tests against multiple backends in one run, including
        third-party backends not included within Alembic itself.
        Third party dialects and extensions are also encouraged to standardize
        on SQLAlchemy's test suite as a basis; see the file README.dialects.rst
        for background on building out from SQLAlchemy's test platform.

    .. change::
        :tags: feature, orm
        :tickets: 2976

        Added a new option to :paramref:`.relationship.innerjoin` which is
        to specify the string ``"nested"``.  When set to ``"nested"`` as opposed
        to ``True``, the "chaining" of joins will parenthesize the inner join on the
        right side of an existing outer join, instead of chaining as a string
        of outer joins.   This possibly should have been the default behavior
        when 0.9 was released, as we introduced the feature of right-nested
        joins in the ORM, however we are keeping it as a non-default for now
        to avoid further surprises.

        .. seealso::

            :ref:`feature_2976`

    .. change::
        :tags: bug, ext
        :tickets: 2810

        Fixed a regression in association proxy caused by :ticket:`2810` which
        caused a user-provided "getter" to no longer receive values of ``None``
        when fetching scalar values from a target that is non-present.  The
        check for None introduced by this change is now moved into the default
        getter, so a user-provided getter will also again receive values of
        None.

    .. change::
        :tags: bug, sql
        :tickets: 2974

        Adjusted the logic which applies names to the .c collection when
        a no-name :class:`.BindParameter` is received, e.g. via :func:`.sql.literal`
        or similar; the "key" of the bind param is used as the key within
        .c. rather than the rendered name.  Since these binds have "anonymous"
        names in any case, this allows individual bound parameters to
        have their own name within a selectable if they are otherwise unlabeled.

    .. change::
        :tags: bug, sql
        :tickets: 2974

        Some changes to how the :attr:`.FromClause.c` collection behaves
        when presented with duplicate columns.  The behavior of emitting a
        warning and replacing the old column with the same name still
        remains to some degree; the replacement in particular is to maintain
        backwards compatibility.  However, the replaced column still remains
        associated with the ``c`` collection now in a collection ``._all_columns``,
        which is used by constructs such as aliases and unions, to deal with
        the set of columns in ``c`` more towards what is actually in the
        list of columns rather than the unique set of key names.  This helps
        with situations where SELECT statements with same-named columns
        are used in unions and such, so that the union can match the columns
        up positionally and also there's some chance of :meth:`.FromClause.corresponding_column`
        still being usable here (it can now return a column that is only
        in selectable.c._all_columns and not otherwise named).
        The new collection is underscored as we still need to decide where this
        list might end up.   Theoretically it
        would become the result of iter(selectable.c), however this would mean
        that the length of the iteration would no longer match the length of
        keys(), and that behavior needs to be checked out.

    .. change::
        :tags: bug, sql

        Fixed issue in new :meth:`.TextClause.columns` method where the ordering
        of columns given positionally would not be preserved.   This could
        have potential impact in positional situations such as applying the
        resulting :class:`.TextAsFrom` object to a union.

    .. change::
        :tags: feature, sql
        :tickets: 2962, 2866

        The new dialect-level keyword argument system for schema-level
        constructs has been enhanced in order to assist with existing
        schemes that rely upon addition of ad-hoc keyword arguments to
        constructs.

        E.g., a construct such as :class:`.Index` will again accept
        ad-hoc keyword arguments within the :attr:`.Index.kwargs` collection,
        after construction::

            idx = Index('a', 'b')
            idx.kwargs['mysql_someargument'] = True

        To suit the use case of allowing custom arguments at construction time,
        the :meth:`.DialectKWArgs.argument_for` method now allows this registration::

            Index.argument_for('mysql', 'someargument', False)

            idx = Index('a', 'b', mysql_someargument=True)

        .. seealso::

            :meth:`.DialectKWArgs.argument_for`

    .. change::
        :tags: bug, orm, engine
        :tickets: 2973

        Fixed bug where events set to listen at the class
        level (e.g. on the :class:`.Mapper` or :class:`.ClassManager`
        level, as opposed to on an individual mapped class, and also on
        :class:`.Connection`) that also made use of internal argument conversion
        (which is most within those categories) would fail to be removable.

    .. change::
        :tags: bug, orm

        Fixed regression from 0.8 where using an option like
        :func:`.orm.lazyload` with the "wildcard" expression, e.g. ``"*"``,
        would raise an assertion error in the case where the query didn't
        contain any actual entities.  This assertion is meant for other cases
        and was catching this one inadvertently.

    .. change::
        :tags: bug, examples

        Fixed bug in the versioned_history example where column-level INSERT
        defaults would prevent history values of NULL from being written.

    .. change::
        :tags: orm, bug, sqlite
        :tickets: 2969

        More fixes to SQLite "join rewriting"; the fix from :ticket:`2967`
        implemented right before the release of 0.9.3 affected the case where
        a UNION contained nested joins in it.   "Join rewriting" is a feature
        with a wide range of possibilities and is the first intricate
        "SQL rewriting" feature we've introduced in years, so we're sort of
        going through a lot of iterations with it (not unlike eager loading
        back in the 0.2/0.3 series, polymorphic loading in 0.4/0.5). We should
        be there soon so thanks for bearing with us :).


.. changelog::
    :version: 0.9.3
    :released: February 19, 2014

    .. change::
        :tags: orm, bug, sqlite
        :tickets: 2967

        Fixed bug in SQLite "join rewriting" where usage of an exists() construct
        would fail to be rewritten properly, such as when the exists is
        mapped to a column_property in an intricate nested-join scenario.
        Also fixed a somewhat related issue where join rewriting would fail
        on the columns clause of the SELECT statement if the targets were
        aliased tables, as opposed to individual aliased columns.

    .. change::
        :tags: sqlite, bug

        The SQLite dialect will now skip unsupported arguments when reflecting
        types; such as if it encounters a string like ``INTEGER(5)``, the
        :class:`.INTEGER` type will be instantiated without the "5" being included,
        based on detecting a ``TypeError`` on the first attempt.

    .. change::
        :tags: sqlite, bug

        Support has been added to SQLite type reflection to fully support
        the "type affinity" contract specified at http://www.sqlite.org/datatype3.html.
        In this scheme, keywords like ``INT``, ``CHAR``, ``BLOB`` or
        ``REAL`` located in the type name generically associate the type with
        one of five affinities.  Pull request courtesy Erich Blume.

        .. seealso::

            :ref:`sqlite_type_reflection`

    .. change::
        :tags: postgresql, feature

        Added the :attr:`.TypeEngine.python_type` convenience accessor onto the
        :class:`.postgresql.ARRAY` type.  Pull request courtesy Alexey Terentev.

    .. change::
        :tags: examples, feature

        Added optional "changed" column to the versioned rows example, as well
        as support for when the versioned :class:`.Table` has an explicit
        :paramref:`~.Table.schema` argument.   Pull request
        courtesy jplaverdure.

    .. change::
        :tags: bug, postgresql
        :tickets: 2946

        Added server version detection to the newly added dialect startup
        query for  "show standard_conforming_strings"; as this variable was
        added as of PG 8.2, we skip the query for PG versions who report a
        version string earlier than that.

    .. change::
        :tags: bug, orm, declarative
        :tickets: 2950

        Fixed bug where :class:`.AbstractConcreteBase` would fail to be
        fully usable within declarative relationship configuration, as its
        string classname would not be available in the registry of classnames
        at mapper configuration time.   The class now explicitly adds itself
        to the class registry, and additionally both :class:`.AbstractConcreteBase`
        as well as :class:`.ConcreteBase` set themselves up *before* mappers
        are configured within the :func:`.configure_mappers` setup, using
        the new :meth:`.MapperEvents.before_configured` event.

    .. change::
        :tags: feature, orm

        Added new :meth:`.MapperEvents.before_configured` event which allows
        an event at the start of :func:`.configure_mappers`, as well
        as ``__declare_first__()`` hook within declarative to complement
        ``__declare_last__()``.

    .. change::
        :tags: bug, mysql, cymysql
        :tickets: 2934

        Fixed bug in cymysql dialect where a version string such as
        ``'33a-MariaDB'`` would fail to parse properly.  Pull request
        courtesy Matt Schmidt.

    .. change::
        :tags: bug, orm
        :tickets: 2949

        Fixed an 0.9 regression where ORM instance or mapper events applied
        to a base class such as a declarative base with the propagate=True
        flag would fail to apply to existing mapped classes which also
        used inheritance due to an assertion.  Additionally, repaired an
        attribute error which could occur during removal of such an event,
        depending on how it was first assigned.

    .. change::
        :tags: bug, ext

        Fixed bug where the :class:`.AutomapBase` class of the
        new automap extension would fail if classes
        were pre-arranged in single or potentially joined inheritance patterns.
        The repaired joined inheritance issue could also potentially apply when
        using :class:`.DeferredReflection` as well.


    .. change::
        :tags: bug, sql

        Fixed regression in new "naming convention" feature where conventions
        would fail if the referred table in a foreign key contained a schema
        name.  Pull request courtesy Thomas Farvour.

    .. change::
        :tags: bug, sql

        Fixed bug where so-called "literal render" of :func:`.bindparam`
        constructs would fail if the bind were constructed with a callable,
        rather than a direct value.  This prevented ORM expressions
        from being rendered with the "literal_binds" compiler flag.

    .. change::
        :tags: bug, orm
        :tickets: 2935

        Improved the initialization logic of composite attributes such that
        calling ``MyClass.attribute`` will not require that the configure
        mappers step has occurred, e.g. it will just work without throwing
        any error.

    .. change::
        :tags: bug, orm
        :tickets: 2932

        More issues with [ticket:2932] first resolved in 0.9.2 where
        using a column key of the form ``<tablename>_<columnname>``
        matching that of an aliased column in the text would still not
        match at the ORM level, which is ultimately due to a core
        column-matching issue.  Additional rules have been added so that the
        column ``_label`` is taken into account when working with a
        :class:`.TextAsFrom` construct or with literal columns.

.. changelog::
    :version: 0.9.2
    :released: February 2, 2014

    .. change::
        :tags: bug, examples

        Added a tweak to the "history_meta" example where the check for
        "history" on a relationship-bound attribute will now no longer emit
        any SQL if the relationship is unloaded.

    .. change::
        :tags: feature, sql

        Added :paramref:`.MetaData.reflect.**dialect_kwargs`
        to support dialect-level reflection options for all :class:`.Table`
        objects reflected.

    .. change::
        :tags: feature, postgresql
        :tickets: 2922

        Added a new dialect-level argument ``postgresql_ignore_search_path``;
        this argument is accepted by both the :class:`.Table` constructor
        as well as by the :meth:`.MetaData.reflect` method.  When in use
        against PostgreSQL, a foreign-key referenced table which specifies
        a remote schema name will retain that schema name even if the name
        is present in the ``search_path``; the default behavior since 0.7.3
        has been that schemas present in ``search_path`` would not be copied
        to reflected :class:`.ForeignKey` objects.  The documentation has been
        updated to describe in detail the behavior of the ``pg_get_constraintdef()``
        function and how the ``postgresql_ignore_search_path`` feature essentially
        determines if we will honor the schema qualification reported by
        this function or not.

        .. seealso::

            :ref:`postgresql_schema_reflection`

    .. change::
        :tags: bug, sql
        :tickets: 2913

        The behavior of :meth:`.Table.tometadata` has been adjusted such that
        the schema target of a :class:`.ForeignKey` will not be changed unless
        that schema matches that of the parent table.  That is, if
        a table "schema_a.user" has a foreign key to "schema_b.order.id",
        the "schema_b" target will be maintained whether or not the
        "schema" argument is passed to :meth:`.Table.tometadata`.  However
        if a table "schema_a.user" refers to "schema_a.order.id", the presence
        of "schema_a" will be updated on both the parent and referred tables.
        This is a behavioral change hence isn't likely to be backported to
        0.8; it is assumed that the previous behavior is pretty buggy
        however and that it's unlikely anyone was relying upon it.

        Additionally, a new parameter has been added
        :paramref:`.Table.tometadata.referred_schema_fn`.  This refers to a
        callable function which will be used to determine the new referred
        schema for any :class:`.ForeignKeyConstraint` encountered in the
        tometadata operation.  This callable can be used to revert to the
        previous behavior or to customize how referred schemas are treated
        on a per-constraint basis.

    .. change::
        :tags: bug, orm
        :tickets: 2932

        Fixed bug in new :class:`.TextAsFrom` construct where :class:`.Column`-
        oriented row lookups were not matching up to the ad-hoc :class:`.ColumnClause`
        objects that :class:`.TextAsFrom` generates, thereby making it not
        usable as a target in :meth:`.Query.from_statement`.  Also fixed
        :meth:`.Query.from_statement` mechanics to not mistake a :class:`.TextAsFrom`
        for a :class:`.Select` construct.  This bug is also an 0.9 regression
        as the :meth:`.Text.columns` method is called to accommodate the
        :paramref:`.text.typemap` argument.

    .. change::
        :tags: feature, sql
        :tickets: 2923

        Added a new feature which allows automated naming conventions to be
        applied to :class:`.Constraint` and :class:`.Index` objects.  Based
        on a recipe in the wiki, the new feature uses schema-events to set up
        names as various schema objects are associated with each other.  The
        events then expose a configuration system through a new argument
        :paramref:`.MetaData.naming_convention`.  This system allows production
        of both simple and custom naming schemes for constraints and indexes
        on a per-:class:`.MetaData` basis.

        .. seealso::

            :ref:`constraint_naming_conventions`

    .. change::
        :tags: bug, orm
        :tickets: 2921

        Added a new directive used within the scope of an attribute "set" operation
        to disable autoflush, in the case that the attribute needs to lazy-load
        the "old" value, as in when replacing one-to-one values or some
        kinds of many-to-one.  A flush at this point otherwise occurs
        at the point that the attribute is None and can cause NULL violations.

    .. change::
        :tags: feature, orm

        Added a new parameter :paramref:`.Operators.op.is_comparison`.  This
        flag allows a custom op from :meth:`.Operators.op` to be considered
        as a "comparison" operator, thus usable for custom
        :paramref:`.relationship.primaryjoin` conditions.

        .. seealso::

            :ref:`relationship_custom_operator`

    .. change::
        :tags: bug, sqlite

        Fixed bug whereby SQLite compiler failed to propagate compiler arguments
        such as "literal binds" into a CAST expression.

    .. change::
        :tags: bug, sql

        Fixed bug whereby binary type would fail in some cases
        if used with a "test" dialect, such as a DefaultDialect or other
        dialect with no DBAPI.

    .. change::
        :tags: bug, sql, py3k

        Fixed bug where "literal binds" wouldn't work with a bound parameter
        that's a binary type.  A similar, but different, issue is fixed
        in 0.8.

    .. change::
        :tags: bug, sql
        :tickets: 2927

        Fixed regression whereby the "annotation" system used by the ORM was leaking
        into the names used by standard functions in :mod:`sqlalchemy.sql.functions`,
        such as ``func.coalesce()`` and ``func.max()``.  Using these functions
        in ORM attributes and thus producing annotated versions of them could
        corrupt the actual function name rendered in the SQL.

    .. change::
        :tags: bug, sql
        :tickets: 2924, 2848

        Fixed 0.9 regression where the new sortable support for :class:`.RowProxy`
        would lead to ``TypeError`` when compared to non-tuple types as it attempted
        to apply tuple() to the "other" object unconditionally.  The
        full range of Python comparison operators have now been implemented on
        :class:`.RowProxy`, using an approach that guarantees a comparison
        system that is equivalent to that of a tuple, and the "other" object
        is only coerced if it's an instance of RowProxy.

    .. change::
        :tags: bug, orm
        :tickets: 2918

        Fixed an 0.9 regression where the automatic aliasing applied by
        :class:`.Query` and in other situations where selects or joins
        were aliased (such as joined table inheritance) could fail if a
        user-defined :class:`.Column` subclass were used in the expression.
        In this case, the subclass would fail to propagate ORM-specific
        "annotations" along needed by the adaptation.  The "expression
        annotations" system has been corrected to account for this case.

    .. change::
        :tags: feature, orm

        Support is improved for supplying a :func:`.join` construct as the
        target of :paramref:`.relationship.secondary` for the purposes
        of creating very complex :func:`.relationship` join conditions.
        The change includes adjustments to query joining, joined eager loading
        to not render a SELECT subquery, changes to lazy loading such that
        the "secondary" target is properly included in the SELECT, and
        changes to declarative to better support specification of a
        join() object with classes as targets.

        The new use case is somewhat experimental, but a new documentation section
        has been added.

        .. seealso::

            :ref:`composite_secondary_join`

    .. change::
        :tags: bug, mysql, sql
        :tickets: 2917

        Added new test coverage for so-called "down adaptions" of SQL types,
        where a more specific type is adapted to a more generic one - this
        use case is needed by some third party tools such as ``sqlacodegen``.
        The specific cases that needed repair within this test suite were that
        of :class:`.mysql.ENUM` being downcast into a :class:`.types.Enum`,
        and that of SQLite date types being cast into generic date types.
        The ``adapt()`` method needed to become more specific here to counteract
        the removal of a "catch all" ``**kwargs`` collection on the base
        :class:`.TypeEngine` class that was removed in 0.9.

    .. change::
        :tags: feature, sql
        :tickets: 2910

        Options can now be specified on a :class:`.PrimaryKeyConstraint` object
        independently of the specification of columns in the table with
        the ``primary_key=True`` flag; use a :class:`.PrimaryKeyConstraint`
        object with no columns in it to achieve this result.

        Previously, an explicit :class:`.PrimaryKeyConstraint` would have the
        effect of those columns marked as ``primary_key=True`` being ignored;
        since this is no longer the case, the :class:`.PrimaryKeyConstraint`
        will now assert that either one style or the other is used to specify
        the columns, or if both are present, that the column lists match
        exactly.  If an inconsistent set of columns in the
        :class:`.PrimaryKeyConstraint`
        and within the :class:`.Table` marked as ``primary_key=True`` are
        present, a warning is emitted, and the list of columns is taken
        only from the :class:`.PrimaryKeyConstraint` alone as was the case
        in previous releases.



        .. seealso::

            :class:`.PrimaryKeyConstraint`

    .. change::
        :tags: feature, sql
        :tickets: 2866

        The system by which schema constructs and certain SQL constructs
        accept dialect-specific keyword arguments has been enhanced.  This
        system includes commonly the :class:`.Table` and :class:`.Index` constructs,
        which accept a wide variety of dialect-specific arguments such as
        ``mysql_engine`` and ``postgresql_where``, as well as the constructs
        :class:`.PrimaryKeyConstraint`, :class:`.UniqueConstraint`,
        :class:`.Update`, :class:`.Insert` and :class:`.Delete`, and also
        newly added kwarg capability to :class:`.ForeignKeyConstraint`
        and :class:`.ForeignKey`.  The change is that participating dialects
        can now specify acceptable argument lists for these constructs, allowing
        an argument error to be raised if an invalid keyword is specified for
        a particular dialect.  If the dialect portion of the keyword is unrecognized,
        a warning is emitted only; while the system will actually make use
        of setuptools entrypoints in order to locate non-local dialects,
        the use case where certain dialect-specific arguments are used
        in an environment where that third-party dialect is uninstalled remains
        supported.  Dialects also have to explicitly opt-in to this system,
        so that external dialects which aren't making use of this system
        will remain unaffected.

    .. change::
        :tags: bug, sql

        A :class:`.UniqueConstraint` created inline with a :class:`.Table`
        that has no columns within it will be skipped.  Pullreq courtesy
        Derek Harland.

    .. change::
        :tags: feature, mssql

        Added an option ``mssql_clustered`` to the :class:`.UniqueConstraint`
        and :class:`.PrimaryKeyConstraint` constructs; on SQL Server, this adds
        the ``CLUSTERED`` keyword to the constraint construct within DDL.
        Pullreq courtesy Derek Harland.

    .. change::
        :tags: bug, sql, orm
        :tickets: 2912

        Fixed the multiple-table "UPDATE..FROM" construct, only usable on
        MySQL, to correctly render the SET clause among multiple columns
        with the same name across tables.  This also changes the name used for
        the bound parameter in the SET clause to "<tablename>_<colname>" for
        the non-primary table only; as this parameter is typically specified
        using the :class:`.Column` object directly this should not have an
        impact on applications.   The fix takes effect for both
        :meth:`.Table.update` as well as :meth:`.Query.update` in the ORM.

    .. change::
        :tags: bug, oracle
        :tickets: 2911

        It's been observed that the usage of a cx_Oracle "outputtypehandler"
        in Python 2.xx in order to coerce string values to Unicode is inordinately
        expensive; even though cx_Oracle is written in C, when you pass the
        Python ``unicode`` primitive to cursor.var() and associate with an output
        handler, the library counts every conversion as a Python function call
        with all the requisite overhead being recorded; this *despite* the fact
        when running in Python 3, all strings are also unconditionally coerced
        to unicode but it does *not* incur this overhead,
        meaning that cx_Oracle is failing to use performant techniques in Py2K.
        As SQLAlchemy cannot easily select for this style of type handler on a
        per-column basis, the handler was assembled unconditionally thereby
        adding the overhead to all string access.

        So this logic has been replaced with SQLAlchemy's own unicode
        conversion system, which now
        only takes effect in Py2K for columns that are requested as unicode.
        When C extensions are used, SQLAlchemy's system appears to be 2-3x faster than
        cx_Oracle's.  Additionally, SQLAlchemy's unicode conversion has been
        enhanced such that when the "conditional" converter is required
        (now needed for the Oracle backend), the check for "already unicode" is now
        performed in C and no longer introduces significant overhead.

        This change has two impacts on the cx_Oracle backend.  One is that
        string values in Py2K which aren't specifically requested with the
        Unicode type or convert_unicode=True will now come back as ``str``,
        not ``unicode`` - this behavior is similar to a backend such as
        MySQL.  Additionally, when unicode values are requested with the cx_Oracle
        backend, if the C extensions are *not* used, there is now an additional
        overhead of an isinstance() check per column.  This tradeoff has been
        made as it can be worked around and no longer places a performance burden
        on the likely majority of Oracle result columns that are non-unicode
        strings.

    .. change::
        :tags: bug, orm
        :tickets: 2908

        Fixed a bug involving the new flattened JOIN structures which
        are used with :func:`.joinedload()` (thereby causing a regression
        in joined eager loading) as well as :func:`.aliased`
        in conjunction with the ``flat=True`` flag and joined-table inheritance;
        basically multiple joins across a "parent JOIN sub" entity using different
        paths to get to a target class wouldn't form the correct ON conditions.
        An adjustment / simplification made in the mechanics of figuring
        out the "left side" of the join in the case of an aliased, joined-inh
        class repairs the issue.

    .. change::
        :tags: bug, mysql

        The MySQL CAST compilation now takes into account aspects of a string
        type such as "charset" and "collation".  While MySQL wants all character-
        based CAST calls to use the CHAR type, we now create a real CHAR
        object at CAST time and copy over all the parameters it has, so that
        an expression like ``cast(x, mysql.TEXT(charset='utf8'))`` will
        render ``CAST(t.col AS CHAR CHARACTER SET utf8)``.

    .. change::
        :tags: bug, mysql
        :tickets: 2906

        Added new "unicode returns" detection to the MySQL dialect and
        to the default dialect system overall, such that any dialect
        can add extra "tests" to the on-first-connect "does this DBAPI
        return unicode directly?" detection. In this case, we are
        adding a check specifically against the "utf8" encoding with
        an explicit "utf8_bin" collation type (after checking that
        this collation is available) to test for some buggy unicode
        behavior observed with MySQLdb version 1.2.3.  While MySQLdb
        has resolved this issue as of 1.2.4, the check here should
        guard against regressions.  The change also allows the "unicode"
        checks to log in the engine logs, which was not previously
        the case.

    .. change::
        :tags: bug, mysql, pool, engine
        :tickets: 2907

        :class:`.Connection` now associates a new
        :class:`.RootTransaction` or :class:`.TwoPhaseTransaction`
        with its immediate :class:`._ConnectionFairy` as a "reset handler"
        for the span of that transaction, which takes over the task
        of calling commit() or rollback() for the "reset on return" behavior
        of :class:`.Pool` if the transaction was not otherwise completed.
        This resolves the issue that a picky transaction
        like that of MySQL two-phase will be
        properly closed out when the connection is closed without an
        explicit rollback or commit (e.g. no longer raises "XAER_RMFAIL"
        in this case - note this only shows up in logging as the exception
        is not propagated within pool reset).
        This issue would arise e.g. when using an orm
        :class:`.Session` with ``twophase`` set, and then
        :meth:`.Session.close` is called without an explicit rollback or
        commit.   The change also has the effect that you will now see
        an explicit "ROLLBACK" in the logs when using a :class:`.Session`
        object in non-autocommit mode regardless of how that session was
        discarded.  Thanks to Jeff Dairiki and Laurence Rowe for isolating
        the issue here.

    .. change::
        :tags: feature, pool, engine

        Added a new pool event :meth:`.PoolEvents.invalidate`.  Called when
        a DBAPI connection is to be marked as "invalidated" and discarded
        from the pool.

    .. change::
        :tags: bug, pool

        The argument names for the :meth:`.PoolEvents.reset` event have been
        renamed to ``dbapi_connection`` and ``connection_record`` in order
        to maintain consistency with all the other pool events.  It is expected
        that any existing listeners for this relatively new and
        seldom-used event are using positional style to receive arguments in
        any case.

    .. change::
        :tags: bug, py3k, cextensions

        Fixed an issue where the C extensions in Py3K are using the wrong API
        to specify the top-level module function, which breaks
        in Python 3.4b2.  Py3.4b2 changes PyMODINIT_FUNC to return
        "void" instead of ``PyObject *``, so we now make sure to use
        "PyMODINIT_FUNC" instead of ``PyObject *`` directly.  Pull request
        courtesy cgohlke.

    .. change::
        :tags: bug, schema

        Restored :class:`sqlalchemy.schema.SchemaVisitor` to the ``.schema``
        module.  Pullreq courtesy Sean Dague.

.. changelog::
    :version: 0.9.1
    :released: January 5, 2014

    .. change::
        :tags: bug, orm, events
        :tickets: 2905

        Fixed regression where using a ``functools.partial()`` with the event
        system would cause a recursion overflow due to usage of inspect.getargspec()
        on it in order to detect a legacy calling signature for certain events,
        and apparently there's no way to do this with a partial object.  Instead
        we skip the legacy check and assume the modern style; the check itself
        now only occurs for the SessionEvents.after_bulk_update and
        SessionEvents.after_bulk_delete events.  Those two events will require
        the new signature style if assigned to a "partial" event listener.

    .. change::
        :tags: feature, orm, extensions

        A new, **experimental** extension :mod:`sqlalchemy.ext.automap` is added.
        This extension expands upon the functionality of Declarative as well as
        the :class:`.DeferredReflection` class to produce a base class which
        automatically generates mapped classes *and relationships* based on
        table metadata.

        .. seealso::

            :ref:`feature_automap`

            :ref:`automap_toplevel`

    .. change::
        :tags: feature, sql

        Conjunctions like :func:`.and_` and :func:`.or_` can now accept
        Python generators as a single argument, e.g.::

            and_(x == y for x, y in tuples)

        The logic here looks for a single argument ``*args`` where the first
        element is an instance of ``types.GeneratorType``.

    .. change::
        :tags: feature, schema

        The :paramref:`.Table.extend_existing` and :paramref:`.Table.autoload_replace`
        parameters are now available on the :meth:`.MetaData.reflect`
        method.

    .. change::
        :tags: bug, orm, declarative

        Fixed an extremely unlikely memory issue where when using
        :class:`.DeferredReflection`
        to define classes pending for reflection, if some subset of those
        classes were discarded before the :meth:`.DeferredReflection.prepare`
        method were called to reflect and map the class, a strong reference
        to the class would remain held within the declarative internals.
        This internal collection of "classes to map" now uses weak
        references against the classes themselves.

    .. change::
        :tags: bug, orm

        Fixed bug where using new :attr:`.Session.info` attribute would fail
        if the ``.info`` argument were only passed to the :class:`.sessionmaker`
        creation call but not to the object itself.  Courtesy Robin Schoonover.

    .. change::
        :tags: bug, orm
        :tickets: 2901

        Fixed regression where we don't check the given name against the
        correct string class when setting up a backref based on a name,
        therefore causing the error "too many values to unpack".  This was
        related to the Py3k conversion.

    .. change::
        :tags: bug, orm, declarative
        :tickets: 2900

        A quasi-regression where apparently in 0.8 you can set a class-level
        attribute on declarative to simply refer directly to an :class:`.InstrumentedAttribute`
        on a superclass or on the class itself, and it
        acts more or less like a synonym; in 0.9, this fails to set up enough
        bookkeeping to keep up with the more liberalized backref logic
        from :ticket:`2789`.  Even though this use case was never directly
        considered, it is now detected by declarative at the "setattr()" level
        as well as when setting up a subclass, and the mirrored/renamed attribute
        is now set up as a :func:`.synonym` instead.

    .. change::
        :tags: bug, orm
        :tickets: 2903

        Fixed regression where we apparently still create an implicit
        alias when saying query(B).join(B.cs), where "C" is a joined inh
        class; however, this implicit alias was created only considering
        the immediate left side, and not a longer chain of joins along different
        joined-inh subclasses of the same base.   As long as we're still
        implicitly aliasing in this case, the behavior is dialed back a bit
        so that it will alias the right side in a wider variety of cases.

.. changelog::
    :version: 0.9.0
    :released: December 30, 2013

    .. change::
        :tags: bug, orm, declarative
        :tickets: 2828

        Declarative does an extra check to detect if the same
        :class:`.Column` is mapped multiple times under different properties
        (which typically should be a :func:`.synonym` instead) or if two
        or more :class:`.Column` objects are given the same name, raising
        a warning if this condition is detected.

    .. change::
        :tags: bug, firebird
        :tickets: 2898

        Changed the queries used by Firebird to list table and view names
        to query from the ``rdb$relations`` view instead of the
        ``rdb$relation_fields`` and ``rdb$view_relations`` views.
        Variants of both the old and new queries are mentioned on many
        FAQ and blogs, however the new queries are taken straight from
        the "Firebird FAQ" which appears to be the most official source
        of info.

    .. change::
        :tags: bug, mysql
        :tickets: 2893

        Improvements to the system by which SQL types generate within
        ``__repr__()``, particularly with regards to the MySQL integer/numeric/
        character types which feature a wide variety of keyword arguments.
        The ``__repr__()`` is important for use with Alembic autogenerate
        for when Python code is rendered in a migration script.

    .. change::
        :tags: feature, postgresql
        :tickets: 2581

        Support for PostgreSQL JSON has been added, using the new
        :class:`.JSON` type.   Huge thanks to Nathan Rice for
        implementing and testing this.

    .. change::
        :tags: bug, sql

        The :func:`.cast` function, when given a plain literal value,
        will now apply the given type to the given literal value on the
        bind parameter side according to the type given to the cast,
        in the same manner as that of the :func:`.type_coerce` function.
        However unlike :func:`.type_coerce`, this only takes effect if a
        non-clauseelement value is passed to :func:`.cast`; an existing typed
        construct will retain its type.

    .. change::
        :tags: bug, postgresql

        Now using psycopg2 UNICODEARRAY extension for handling unicode arrays
        with psycopg2 + normal "native unicode" mode, in the same way the
        UNICODE extension is used.

    .. change::
        :tags: bug, sql
        :tickets: 2883

        The :class:`.ForeignKey` class more aggressively checks the given
        column argument.   If not a string, it checks that the object is
        at least a :class:`.ColumnClause`, or an object that resolves to one,
        and that the ``.table`` attribute, if present, refers to a
        :class:`.TableClause` or subclass, and not something like an
        :class:`.Alias`.  Otherwise, a :class:`.ArgumentError` is raised.


    .. change::
        :tags: feature, orm

        The :class:`.exc.StatementError` or DBAPI-related subclass
        now can accommodate additional information about the "reason" for
        the exception; the :class:`.Session` now adds some detail to it
        when the exception occurs within an autoflush.  This approach
        is taken as opposed to combining :class:`.FlushError` with
        a Python 3 style "chained exception" approach so as to maintain
        compatibility both with Py2K code as well as code that already
        catches ``IntegrityError`` or similar.

    .. change::
        :tags: feature, postgresql

        Added support for PostgreSQL TSVECTOR via the
        :class:`.postgresql.TSVECTOR` type.  Pull request courtesy
        Noufal Ibrahim.

    .. change::
        :tags: feature, engine
        :tickets: 2875

        The :func:`.engine_from_config` function has been improved so that
        we will be able to parse dialect-specific arguments from string
        configuration dictionaries.  Dialect classes can now provide their
        own list of parameter types and string-conversion routines.
        The feature is not yet used by the built-in dialects, however.

    .. change::
        :tags: bug, sql
        :tickets: 2879

        The precedence rules for the :meth:`.ColumnOperators.collate` operator
        have been modified, such that the COLLATE operator is now of lower
        precedence than the comparison operators.  This has the effect that
        a COLLATE applied to a comparison will not render parenthesis
        around the comparison, which is not parsed by backends such as
        MSSQL.  The change is backwards incompatible for those setups that
        were working around the issue by applying :meth:`.Operators.collate`
        to an individual element of the comparison expression,
        rather than the comparison expression as a whole.

        .. seealso::

            :ref:`migration_2879`

    .. change::
        :tags: bug, orm, declarative
        :tickets: 2865

        The :class:`.DeferredReflection` class has been enhanced to provide
        automatic reflection support for the "secondary" table referred
        to by a :func:`.relationship`.   "secondary", when specified
        either as a string table name, or as a :class:`.Table` object with
        only a name and :class:`.MetaData` object will also be included
        in the reflection process when :meth:`.DeferredReflection.prepare`
        is called.

    .. change::
        :tags: feature, orm, backrefs
        :tickets: 1535

        Added new argument ``include_backrefs=True`` to the
        :func:`.validates` function; when set to False, a validation event
        will not be triggered if the event was initated as a backref to
        an attribute operation from the other side.

        .. seealso::

            :ref:`feature_1535`

    .. change::
        :tags: bug, orm, collections, py3k

        Added support for the Python 3 method ``list.clear()`` within
        the ORM collection instrumentation system; pull request
        courtesy Eduardo Schettino.

    .. change::
        :tags: bug, postgresql
        :tickets: 2878

        Fixed bug where values within an ENUM weren't escaped for single
        quote signs.   Note that this is backwards-incompatible for existing
        workarounds that manually escape the single quotes.

        .. seealso::

            :ref:`migration_2878`

    .. change::
        :tags: bug, orm, declarative

        Fixed bug where in Py2K a unicode literal would not be accepted
        as the string name of a class or other argument within
        declarative using :func:`.relationship`.

    .. change::
        :tags: feature, sql
        :tickets: 2877, 2882

        New improvements to the :func:`.text` construct, including
        more flexible ways to set up bound parameters and return types;
        in particular, a :func:`.text` can now be turned into a full
        FROM-object, embeddable in other statements as an alias or CTE
        using the new method :meth:`.TextClause.columns`.   The :func:`.text`
        construct can also render "inline" bound parameters when the construct
        is compiled in a "literal bound" context.

        .. seealso::

            :ref:`feature_2877`

    .. change::
        :tags: feature, sql

        A new API for specifying the ``FOR UPDATE`` clause of a ``SELECT``
        is added with the new :meth:`.GenerativeSelect.with_for_update` method.
        This method supports a more straightforward system of setting
        dialect-specific options compared to the ``for_update`` keyword
        argument of :func:`.select`, and also includes support for the
        SQL standard ``FOR UPDATE OF`` clause.   The ORM also includes
        a new corresponding method :meth:`.Query.with_for_update`.
        Pull request courtesy Mario Lassnig.

        .. seealso::

            :ref:`feature_github_42`

    .. change::
        :tags: feature, orm

        A new API for specifying the ``FOR UPDATE`` clause of a ``SELECT``
        is added with the new :meth:`.Query.with_for_update` method,
        to complement the new :meth:`.GenerativeSelect.with_for_update` method.
        Pull request courtesy Mario Lassnig.

        .. seealso::

            :ref:`feature_github_42`

    .. change::
        :tags: bug, engine
        :tickets: 2873

        The :func:`.create_engine` routine and the related
        :func:`.make_url` function no longer considers the ``+`` sign
        to be a space within the password field.  The parsing has been
        adjusted to match RFC 1738 exactly, in that both ``username``
        and ``password`` expect only ``:``, ``@``, and ``/`` to be
        encoded.

        .. seealso::

            :ref:`migration_2873`


    .. change::
        :tags: bug, orm
        :tickets: 2872

        Some refinements to the :class:`.AliasedClass` construct with regards
        to descriptors, like hybrids, synonyms, composites, user-defined
        descriptors, etc.  The attribute
        adaptation which goes on has been made more robust, such that if a descriptor
        returns another instrumented attribute, rather than a compound SQL
        expression element, the operation will still proceed.
        Additionally, the "adapted" operator will retain its class; previously,
        a change in class from ``InstrumentedAttribute`` to ``QueryableAttribute``
        (a superclass) would interact with Python's operator system such that
        an expression like ``aliased(MyClass.x) > MyClass.x`` would reverse itself
        to read ``myclass.x < myclass_1.x``.   The adapted attribute will also
        refer to the new :class:`.AliasedClass` as its parent which was not
        always the case before.

    .. change::
        :tags: feature, sql
        :tickets: 2867

        The precision used when coercing a returned floating point value to
        Python ``Decimal`` via string is now configurable.  The
        flag ``decimal_return_scale`` is now supported by all :class:`.Numeric`
        and :class:`.Float` types, which will ensure this many digits are taken
        from the native floating point value when it is converted to string.
        If not present, the type will make use of the value of ``.scale``, if
        the type supports this setting and it is non-None.  Otherwise the original
        default length of 10 is used.

        .. seealso::

            :ref:`feature_2867`

    .. change::
        :tags: bug, schema
        :tickets: 2868

        Fixed a regression caused by :ticket:`2812` where the repr() for
        table and column names would fail if the name contained non-ascii
        characters.

    .. change::
        :tags: bug, engine
        :tickets: 2848

        The :class:`.RowProxy` object is now sortable in Python as a regular
        tuple is; this is accomplished via ensuring tuple() conversion on
        both sides within the ``__eq__()`` method as well as
        the addition of a ``__lt__()`` method.

        .. seealso::

            :ref:`migration_2848`

    .. change::
        :tags: bug, orm
        :tickets: 2833

        The ``viewonly`` flag on :func:`.relationship` will now prevent
        attribute history from being written on behalf of the target attribute.
        This has the effect of the object not being written to the
        Session.dirty list if it is mutated.  Previously, the object would
        be present in Session.dirty, but no change would take place on behalf
        of the modified attribute during flush.   The attribute still emits
        events such as backref events and user-defined events and will still
        receive mutations from backrefs.

        .. seealso::

            :ref:`migration_2833`

    .. change::
        :tags: bug, orm

        Added support for new :attr:`.Session.info` attribute to
        :class:`.scoped_session`.

    .. change::
        :tags: removed

        The "informix" and "informixdb" dialects have been removed; the code
        is now available as a separate repository on Bitbucket.   The IBM-DB
        project has provided production-level Informix support since the
        informixdb dialect was first added.

    .. change::
        :tags: bug, orm

        Fixed bug where usage of new :class:`.Bundle` object would cause
        the :attr:`.Query.column_descriptions` attribute to fail.

    .. change::
        :tags: bug, examples

        Fixed bug which prevented history_meta recipe from working with
        joined inheritance schemes more than one level deep.

    .. change::
        :tags: bug, orm, sql, sqlite
        :tickets: 2858

        Fixed a regression introduced by the join rewriting feature of
        :ticket:`2369` and :ticket:`2587` where a nested join with one side
        already an aliased select would fail to translate the ON clause on the
        outside correctly; in the ORM this could be seen when using a
        SELECT statement as a "secondary" table.

.. changelog::
    :version: 0.9.0b1
    :released: October 26, 2013

    .. change::
        :tags: feature, orm
        :tickets: 2810

        The association proxy now returns ``None`` when fetching a scalar
        attribute off of a scalar relationship, where the scalar relationship
        itself points to ``None``, instead of raising an ``AttributeError``.

        .. seealso::

            :ref:`migration_2810`

    .. change::
        :tags: feature, sql, postgresql, mysql
        :tickets: 2183

        The PostgreSQL and MySQL dialects now support reflection/inspection
        of foreign key options, including ON UPDATE, ON DELETE.  PostgreSQL
        also reflects MATCH, DEFERRABLE, and INITIALLY.  Courtesy ijl.

    .. change::
        :tags: bug, mysql
        :tickets: 2839

        Fix and test parsing of MySQL foreign key options within reflection;
        this complements the work in :ticket:`2183` where we begin to support
        reflection of foreign key options such as ON UPDATE/ON DELETE
        cascade.

    .. change::
        :tags: bug, orm
        :tickets: 2787

        :func:`.attributes.get_history()` when used with a scalar column-mapped
        attribute will now honor the "passive" flag
        passed to it; as this defaults to ``PASSIVE_OFF``, the function will
        by default query the database if the value is not present.
        This is a behavioral change vs. 0.8.

        .. seealso::

            :ref:`change_2787`

    .. change::
        :tags: feature, orm
        :tickets: 2787

        Added new method :meth:`.AttributeState.load_history`, works like
        :attr:`.AttributeState.history` but also fires loader callables.

        .. seealso::

            :ref:`change_2787`


    .. change::
        :tags: feature, sql
        :tickets: 2850

        A :func:`.bindparam` construct with a "null" type (e.g. no type
        specified) is now copied when used in a typed expression, and the
        new copy is assigned the actual type of the compared column.  Previously,
        this logic would occur on the given :func:`.bindparam` in place.
        Additionally, a similar process now occurs for :func:`.bindparam` constructs
        passed to :meth:`.ValuesBase.values` for an :class:`.Insert` or
        :class:`.Update` construct, within the compilation phase of the
        construct.

        These are both subtle behavioral changes which may impact some
        usages.

        .. seealso::

            :ref:`migration_2850`

    .. change::
        :tags: feature, sql
        :tickets: 2804, 2823, 2734

        An overhaul of expression handling for special symbols particularly
        with conjunctions, e.g.
        ``None`` :func:`.expression.null` :func:`.expression.true`
        :func:`.expression.false`, including consistency in rendering NULL
        in conjunctions, "short-circuiting" of :func:`.and_` and :func:`.or_`
        expressions which contain boolean constants, and rendering of
        boolean constants and expressions as compared to "1" or "0" for backends
        that don't feature ``true``/``false`` constants.

        .. seealso::

            :ref:`migration_2804`

    .. change::
        :tags: feature, sql
        :tickets: 2838

        The typing system now handles the task of rendering "literal bind" values,
        e.g. values that are normally bound parameters but due to context must
        be rendered as strings, typically within DDL constructs such as
        CHECK constraints and indexes (note that "literal bind" values
        become used by DDL as of :ticket:`2742`).  A new method
        :meth:`.TypeEngine.literal_processor` serves as the base, and
        :meth:`.TypeDecorator.process_literal_param` is added to allow wrapping
        of a native literal rendering method.

        .. seealso::

            :ref:`change_2838`

    .. change::
        :tags: feature, sql
        :tickets: 2716

        The :meth:`.Table.tometadata` method now produces copies of
        all :attr:`.SchemaItem.info` dictionaries from all :class:`.SchemaItem`
        objects within the structure including columns, constraints,
        foreign keys, etc.   As these dictionaries
        are copies, they are independent of the original dictionary.
        Previously, only the ``.info`` dictionary of :class:`.Column` was transferred
        within this operation, and it was only linked in place, not copied.

    .. change::
        :tags: feature, postgresql
        :tickets: 2840

        Added support for rendering ``SMALLSERIAL`` when a :class:`.SmallInteger`
        type is used on a primary key autoincrement column, based on server
        version detection of PostgreSQL version 9.2 or greater.

    .. change::
        :tags: feature, mysql
        :tickets: 2817

        The MySQL :class:`.mysql.SET` type now features the same auto-quoting
        behavior as that of :class:`.mysql.ENUM`.  Quotes are not required when
        setting up the value, but quotes that are present will be auto-detected
        along with a warning.  This also helps with Alembic where
        the SET type doesn't render with quotes.

    .. change::
        :tags: feature, sql

        The ``default`` argument of :class:`.Column` now accepts a class
        or object method as an argument, in addition to a standalone function;
        will properly detect if the "context" argument is accepted or not.

    .. change::
        :tags: bug, sql
        :tickets: 2835

        The "name" attribute is set on :class:`.Index` before the "attach"
        events are called, so that attachment events can be used to dynamically
        generate a name for the index based on the parent table and/or
        columns.

    .. change::
        :tags: bug, engine
        :tickets: 2748

        The method signature of :meth:`.Dialect.reflecttable`, which in
        all known cases is provided by :class:`.DefaultDialect`, has been
        tightened to expect ``include_columns`` and ``exclude_columns``
        arguments without any kw option, reducing ambiguity - previously
        ``exclude_columns`` was missing.

    .. change::
        :tags: bug, sql
        :tickets: 2831

        The erroneous kw arg "schema" has been removed from the :class:`.ForeignKey`
        object. this was an accidental commit that did nothing; a warning is raised
        in 0.8.3 when this kw arg is used.

    .. change::
        :tags: feature, orm
        :tickets: 1418

        Added a new load option :func:`.orm.load_only`.  This allows a series
        of column names to be specified as loading "only" those attributes,
        deferring the rest.

    .. change::
        :tags: feature, orm
        :tickets: 1418

        The system of loader options has been entirely rearchitected to build
        upon a much more comprehensive base, the :class:`.Load` object.  This
        base allows any common loader option like :func:`.joinedload`,
        :func:`.defer`, etc. to be used in a "chained" style for the purpose
        of specifying options down a path, such as ``joinedload("foo").subqueryload("bar")``.
        The new system supersedes the usage of dot-separated path names,
        multiple attributes within options, and the usage of ``_all()`` options.

        .. seealso::

            :ref:`feature_1418`

    .. change::
        :tags: feature, orm
        :tickets: 2824

        The :func:`.composite` construct now maintains the return object
        when used in a column-oriented :class:`.Query`, rather than expanding
        out into individual columns.  This makes use of the new :class:`.Bundle`
        feature internally.  This behavior is backwards incompatible; to
        select from a composite column which will expand out, use
        ``MyClass.some_composite.clauses``.

        .. seealso::

            :ref:`migration_2824`

    .. change::
        :tags: feature, orm
        :tickets: 2824

        A new construct :class:`.Bundle` is added, which allows for specification
        of groups of column expressions to a :class:`.Query` construct.
        The group of columns are returned as a single tuple by default.  The
        behavior of :class:`.Bundle` can be overridden however to provide
        any sort of result processing to the returned row.  The behavior
        of :class:`.Bundle` is also embedded into composite attributes now
        when they are used in a column-oriented :class:`.Query`.

        .. seealso::

            :ref:`change_2824`

            :ref:`migration_2824`

    .. change::
        :tags: bug, sql
        :tickets: 2812

        A rework to the way that "quoted" identifiers are handled, in that
        instead of relying upon various ``quote=True`` flags being passed around,
        these flags are converted into rich string objects with quoting information
        included at the point at which they are passed to common schema constructs
        like :class:`.Table`, :class:`.Column`, etc.   This solves the issue
        of various methods that don't correctly honor the "quote" flag such
        as :meth:`.Engine.has_table` and related methods.  The :class:`.quoted_name`
        object is a string subclass that can also be used explicitly if needed;
        the object will hold onto the quoting preferences passed and will
        also bypass the "name normalization" performed by dialects that
        standardize on uppercase symbols, such as Oracle, Firebird and DB2.
        The upshot is that the "uppercase" backends can now work with force-quoted
        names, such as lowercase-quoted names and new reserved words.

        .. seealso::

            :ref:`change_2812`

    .. change::
        :tags: feature, orm
        :tickets: 2793

        The ``version_id_generator`` parameter of ``Mapper`` can now be specified
        to rely upon server generated version identifiers, using triggers
        or other database-provided versioning features, or via an optional programmatic
        value, by setting ``version_id_generator=False``.
        When using a server-generated version identifier, the ORM will use RETURNING when
        available to immediately
        load the new version value, else it will emit a second SELECT.

    .. change::
        :tags: feature, orm
        :tickets: 2793

        The ``eager_defaults`` flag of :class:`.Mapper` will now allow the
        newly generated default values to be fetched using an inline
        RETURNING clause, rather than a second SELECT statement, for backends
        that support RETURNING.

    .. change::
        :tags: feature, core
        :tickets: 2793

        Added a new variant to :meth:`.UpdateBase.returning` called
        :meth:`.ValuesBase.return_defaults`; this allows arbitrary columns
        to be added to the RETURNING clause of the statement without interfering
        with the compilers usual "implicit returning" feature, which is used to
        efficiently fetch newly generated primary key values.  For supporting
        backends, a dictionary of all fetched values is present at
        :attr:`.ResultProxy.returned_defaults`.

    .. change::
        :tags: bug, mysql

        Improved support for the cymysql driver, supporting version 0.6.5,
        courtesy Hajime Nakagami.

    .. change::
        :tags: general

        A large refactoring of packages has reorganized
        the import structure of many Core modules as well as some aspects
        of the ORM modules.  In particular ``sqlalchemy.sql`` has been broken
        out into several more modules than before so that the very large size
        of ``sqlalchemy.sql.expression`` is now pared down.   The effort
        has focused on a large reduction in import cycles.   Additionally,
        the system of API functions in ``sqlalchemy.sql.expression`` and
        ``sqlalchemy.orm`` has been reorganized to eliminate redundancy
        in documentation between the functions vs. the objects they produce.

    .. change::
        :tags: orm, feature, orm

        Added a new attribute :attr:`.Session.info` to :class:`.Session`;
        this is a dictionary where applications can store arbitrary
        data local to a :class:`.Session`.
        The contents of :attr:`.Session.info` can be also be initialized
        using the ``info`` argument of :class:`.Session` or
        :class:`.sessionmaker`.


    .. change::
        :tags: feature, general, py3k
        :tickets: 2161

        The C extensions are ported to Python 3 and will build under
        any supported CPython 2 or 3 environment.

    .. change::
        :tags: feature, orm
        :tickets: 2268

        Removal of event listeners is now implemented.    The feature is
        provided via the :func:`.event.remove` function.

        .. seealso::

            :ref:`feature_2268`

    .. change::
        :tags: feature, orm
        :tickets: 2789

        The mechanism by which attribute events pass along an
        :class:`.AttributeImpl` as an "initiator" token has been changed;
        the object is now an event-specific object called :class:`.attributes.Event`.
        Additionally, the attribute system no longer halts events based
        on a matching "initiator" token; this logic has been moved to be
        specific to ORM backref event handlers, which are the typical source
        of the re-propagation of an attribute event onto subsequent append/set/remove
        operations.  End user code which emulates the behavior of backrefs
        must now ensure that recursive event propagation schemes are halted,
        if the scheme does not use the backref handlers.   Using this new system,
        backref handlers can now perform a
        "two-hop" operation when an object is appended to a collection,
        associated with a new many-to-one, de-associated with the previous
        many-to-one, and then removed from a previous collection.   Before this
        change, the last step of removal from the previous collection would
        not occur.

        .. seealso::

            :ref:`migration_2789`

    .. change::
        :tags: feature, sql
        :tickets: 722

        Added new method to the :func:`.insert` construct
        :meth:`.Insert.from_select`.  Given a list of columns and
        a selectable, renders ``INSERT INTO (table) (columns) SELECT ..``.
        While this feature is highlighted as part of 0.9 it is also
        backported to 0.8.3.

        .. seealso::

            :ref:`feature_722`

    .. change::
        :tags: feature, engine
        :tickets: 2770

        New events added to :class:`.ConnectionEvents`:

        * :meth:`.ConnectionEvents.engine_connect`
        * :meth:`.ConnectionEvents.set_connection_execution_options`
        * :meth:`.ConnectionEvents.set_engine_execution_options`

    .. change::
        :tags: bug, sql
        :tickets: 1765

        The resolution of :class:`.ForeignKey` objects to their
        target :class:`.Column` has been reworked to be as
        immediate as possible, based on the moment that the
        target :class:`.Column` is associated with the same
        :class:`.MetaData` as this :class:`.ForeignKey`, rather
        than waiting for the first time a join is constructed,
        or similar. This along with other improvements allows
        earlier detection of some foreign key configuration
        issues.  Also included here is a rework of the
        type-propagation system, so that
        it should be reliable now to set the type as ``None``
        on any :class:`.Column` that refers to another via
        :class:`.ForeignKey` - the type will be copied from the
        target column as soon as that other column is associated,
        and now works for composite foreign keys as well.

        .. seealso::

            :ref:`migration_1765`

    .. change::
        :tags: feature, sql
        :tickets: 2744, 2734

        Provided a new attribute for :class:`.TypeDecorator`
        called :attr:`.TypeDecorator.coerce_to_is_types`,
        to make it easier to control how comparisons using
        ``==`` or ``!=`` to ``None`` and boolean types goes
        about producing an ``IS`` expression, or a plain
        equality expression with a bound parameter.

    .. change::
        :tags: feature, pool
        :tickets: 2752

        Added pool logging for "rollback-on-return" and the less used
        "commit-on-return".  This is enabled with the rest of pool
        "debug" logging.

    .. change::
        :tags: bug, orm, associationproxy
        :tickets: 2751

        Added additional criterion to the ==, != comparators, used with
        scalar values, for comparisons to None to also take into account
        the association record itself being non-present, in addition to the
        existing test for the scalar endpoint on the association record
        being NULL.  Previously, comparing ``Cls.scalar == None`` would return
        records for which ``Cls.associated`` were present and
        ``Cls.associated.scalar`` is None, but not rows for which
        ``Cls.associated`` is non-present.  More significantly, the
        inverse operation ``Cls.scalar != None`` *would* return ``Cls``
        rows for which ``Cls.associated`` was non-present.

        The case for ``Cls.scalar != 'somevalue'`` is also modified
        to act more like a direct SQL comparison; only rows for
        which ``Cls.associated`` is present and ``Associated.scalar``
        is non-NULL and not equal to ``'somevalue'`` are returned.
        Previously, this would be a simple ``NOT EXISTS``.

        Also added a special use case where you
        can call ``Cls.scalar.has()`` with no arguments,
        when ``Cls.scalar`` is a column-based value - this returns whether or
        not ``Cls.associated`` has any rows present, regardless of whether
        or not ``Cls.associated.scalar`` is NULL or not.

        .. seealso::

            :ref:`migration_2751`


    .. change::
        :tags: feature, orm
        :tickets: 2587

        A major change regarding how the ORM constructs joins where
        the right side is itself a join or left outer join.   The ORM
        is now configured to allow simple nesting of joins of
        the form ``a JOIN (b JOIN c ON b.id=c.id) ON a.id=b.id``,
        rather than forcing the right side into a ``SELECT`` subquery.
        This should allow significant performance improvements on most
        backends, most particularly MySQL.   The one database backend
        that has for many years held back this change, SQLite, is now addressed by
        moving the production of the ``SELECT`` subquery from the
        ORM to the SQL compiler; so that a right-nested join on SQLite will still
        ultimately render with a ``SELECT``, while all other backends
        are no longer impacted by this workaround.

        As part of this change, a new argument ``flat=True`` has been added
        to the :func:`.orm.aliased`, :meth:`.Join.alias`, and
        :func:`.orm.with_polymorphic` functions, which allows an "alias" of a
        JOIN to be produced which applies an anonymous alias to each component
        table within the join, rather than producing a subquery.

        .. seealso::

            :ref:`feature_joins_09`


    .. change::
        :tags: bug, orm
        :tickets: 2369

        Fixed an obscure bug where the wrong results would be
        fetched when joining/joinedloading across a many-to-many
        relationship to a single-table-inheriting
        subclass with a specific discriminator value, due to "secondary"
        rows that would come back.  The "secondary" and right-side
        tables are now inner joined inside of parenthesis for all
        ORM joins on many-to-many relationships so that the left->right
        join can accurately filtered.  This change was made possible
        by finally addressing the issue with right-nested joins
        outlined in :ticket:`2587`.

        .. seealso::

            :ref:`feature_joins_09`

    .. change::
        :tags: bug, mssql, pyodbc
        :tickets: 2355

        Fixes to MSSQL with Python 3 + pyodbc, including that statements
        are passed correctly.

    .. change::
        :tags: feature, sql
        :tickets: 1068

        A :func:`~sqlalchemy.sql.expression.label` construct will now render as its name alone
        in an ``ORDER BY`` clause, if that label is also referred to
        in the columns clause of the select, instead of rewriting the
        full expression.  This gives the database a better chance to
        optimize the evaluation of the same expression in two different
        contexts.

        .. seealso::

            :ref:`migration_1068`

    .. change::
        :tags: feature, firebird
        :tickets: 2504

        The ``fdb`` dialect is now the default dialect when
        specified without a dialect qualifier, i.e. ``firebird://``,
        per the Firebird project publishing ``fdb`` as their
        official Python driver.

    .. change::
    	:tags: feature, general, py3k
      	:tickets: 2671

        The codebase is now "in-place" for Python
        2 and 3, the need to run 2to3 has been removed.
        Compatibility is now against Python 2.6 on forward.

    .. change::
    	:tags: feature, oracle, py3k

    	The Oracle unit tests with cx_oracle now pass
    	fully under Python 3.

    .. change::
        :tags: bug, orm
        :tickets: 2736

        The "auto-aliasing" behavior of the :meth:`.Query.select_from`
        method has been turned off.  The specific behavior is now
        available via a new method :meth:`.Query.select_entity_from`.
        The auto-aliasing behavior here was never well documented and
        is generally not what's desired, as :meth:`.Query.select_from`
        has become more oriented towards controlling how a JOIN is
        rendered.  :meth:`.Query.select_entity_from` will also be made
        available in 0.8 so that applications which rely on the auto-aliasing
        can shift their applications to use this method.

        .. seealso::

            :ref:`migration_2736`
