ORM 查询指南设置：单表继承

此页面说明了 单表继承 示例中使用的映射和fixture数据，这些示例位于 继承映射的 SELECT 语句编写 文档的 ORM 查询指南 中。

>>> from sqlalchemy import create_engine
>>> from sqlalchemy import ForeignKey
>>> from sqlalchemy.orm import DeclarativeBase
>>> from sqlalchemy.orm import Mapped
>>> from sqlalchemy.orm import mapped_column
>>> from sqlalchemy.orm import relationship
>>> from sqlalchemy.orm import Session
>>>
>>>
>>> class Base(DeclarativeBase):
...     pass
>>> class Employee(Base):
...     __tablename__ = "employee"
...     id: Mapped[int] = mapped_column(primary_key=True)
...     name: Mapped[str]
...     type: Mapped[str]
...
...     def __repr__(self):
...         return f"{self.__class__.__name__}({self.name!r})"
...
...     __mapper_args__ = {
...         "polymorphic_identity": "employee",
...         "polymorphic_on": "type",
...     }
>>> class Manager(Employee):
...     manager_name: Mapped[str] = mapped_column(nullable=True)
...     __mapper_args__ = {
...         "polymorphic_identity": "manager",
...     }
>>> class Engineer(Employee):
...     engineer_info: Mapped[str] = mapped_column(nullable=True)
...     __mapper_args__ = {
...         "polymorphic_identity": "engineer",
...     }
>>>
>>> engine = create_engine("sqlite://", echo=True)
>>>
>>> Base.metadata.create_all(engine)
BEGIN ...

>>> conn = engine.connect()
>>> from sqlalchemy.orm import Session
>>> session = Session(conn)
>>> session.add_all(
...     [
...         Manager(
...             name="Mr. Krabs",
...             manager_name="Eugene H. Krabs",
...         ),
...         Engineer(name="SpongeBob", engineer_info="Krabby Patty Master"),
...         Engineer(
...             name="Squidward",
...             engineer_info="Senior Customer Engagement Engineer",
...         ),
...     ],
... )
>>> session.commit()
BEGIN ...