Release: 1.4.31 | Release Date: January 20, 2022

# SQLAlchemy 1.4 Documentation

# Source code for examples.inheritance.single

    """Single-table (table-per-hierarchy) inheritance example."""

    from sqlalchemy import Column
    from sqlalchemy import create_engine
    from sqlalchemy import ForeignKey
    from sqlalchemy import inspect
    from sqlalchemy import Integer
    from sqlalchemy import or_
    from sqlalchemy import String
    from sqlalchemy.ext.declarative import declarative_base
    from sqlalchemy.ext.declarative import declared_attr
    from sqlalchemy.orm import relationship
    from sqlalchemy.orm import Session
    from sqlalchemy.orm import with_polymorphic

    Base = declarative_base()

    class Company(Base):
        __tablename__ = "company"
        id = Column(Integer, primary_key=True)
        name = Column(String(50))

        employees = relationship(
            "Person", back_populates="company", cascade="all, delete-orphan"
        )

        def __repr__(self):
            return "Company %s" % self.name

    class Person(Base):
        __tablename__ = "person"
        id = Column(Integer, primary_key=True)
        company_id = Column(ForeignKey("company.id"))
        name = Column(String(50))
        type = Column(String(50))

        company = relationship("Company", back_populates="employees")

        __mapper_args__ = {
            "polymorphic_identity": "person",
            "polymorphic_on": type,
        }

        def __repr__(self):
            return "Ordinary person %s" % self.name

    class Engineer(Person):

        engineer_name = Column(String(30))
        primary_language = Column(String(30))

        # illustrate a single-inh "conflicting" column declaration;
        # see https://docs.sqlalchemy.org/en/latest/orm/extensions/
        #       declarative/inheritance.html#resolving-column-conflicts
        @declared_attr
        def status(cls):
            return Person.__table__.c.get("status", Column(String(30)))

        __mapper_args__ = {"polymorphic_identity": "engineer"}

        def __repr__(self):
            return (
                "Engineer %s, status %s, engineer_name %s, "
                "primary_language %s"
                % (
                    self.name,
                    self.status,
                    self.engineer_name,
                    self.primary_language,
                )
            )

    class Manager(Person):
        manager_name = Column(String(30))

        @declared_attr
        def status(cls):
            return Person.__table__.c.get("status", Column(String(30)))

        __mapper_args__ = {"polymorphic_identity": "manager"}

        def __repr__(self):
            return "Manager %s, status %s, manager_name %s" % (
                self.name,
                self.status,
                self.manager_name,
            )

    engine = create_engine("sqlite://", echo=True)
    Base.metadata.create_all(engine)

    session = Session(engine)

    c = Company(
        name="company1",
        employees=[
            Manager(
                name="pointy haired boss", status="AAB", manager_name="manager1"
            ),
            Engineer(
                name="dilbert",
                status="BBA",
                engineer_name="engineer1",
                primary_language="java",
            ),
            Person(name="joesmith"),
            Engineer(
                name="wally",
                status="CGG",
                engineer_name="engineer2",
                primary_language="python",
            ),
            Manager(name="jsmith", status="ABA", manager_name="manager2"),
        ],
    )
    session.add(c)

    session.commit()

    c = session.query(Company).get(1)
    for e in c.employees:
        print(e, inspect(e).key, e.company)
    assert set([e.name for e in c.employees]) == set(
        ["pointy haired boss", "dilbert", "joesmith", "wally", "jsmith"]
    )
    print("\n")

    dilbert = session.query(Person).filter_by(name="dilbert").one()
    dilbert2 = session.query(Engineer).filter_by(name="dilbert").one()
    assert dilbert is dilbert2

    dilbert.engineer_name = "hes dilbert!"

    session.commit()

    c = session.query(Company).get(1)
    for e in c.employees:
        print(e)

    # query using with_polymorphic.
    eng_manager = with_polymorphic(Person, [Engineer, Manager])
    print(
        session.query(eng_manager)
        .filter(
            or_(
                eng_manager.Engineer.engineer_name == "engineer1",
                eng_manager.Manager.manager_name == "manager2",
            )
        )
        .all()
    )

    # illustrate join from Company,
    eng_manager = with_polymorphic(Person, [Engineer, Manager])
    print(
        session.query(Company)
        .join(Company.employees.of_type(eng_manager))
        .filter(
            or_(
                eng_manager.Engineer.engineer_name == "engineer1",
                eng_manager.Manager.manager_name == "manager2",
            )
        )
        .all()
    )

    session.commit()