ORM 查询指南设置：联合继承

本页介绍了 联合表继承 示例中使用的映射和固定数据，这些示例在 为继承映射编写 SELECT 语句 文档中，该文档属于 ORM 查询指南。

>>> from typing import List
>>> 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 Company(Base):
...     __tablename__ = "company"
...     id: Mapped[int] = mapped_column(primary_key=True)
...     name: Mapped[str]
...     employees: Mapped[List["Employee"]] = relationship(back_populates="company")
>>>
>>> class Employee(Base):
...     __tablename__ = "employee"
...     id: Mapped[int] = mapped_column(primary_key=True)
...     name: Mapped[str]
...     type: Mapped[str]
...     company_id: Mapped[int] = mapped_column(ForeignKey("company.id"))
...     company: Mapped[Company] = relationship(back_populates="employees")
...
...     def __repr__(self):
...         return f"{self.__class__.__name__}({self.name!r})"
...
...     __mapper_args__ = {
...         "polymorphic_identity": "employee",
...         "polymorphic_on": "type",
...     }
>>>
>>> class Manager(Employee):
...     __tablename__ = "manager"
...     id: Mapped[int] = mapped_column(ForeignKey("employee.id"), primary_key=True)
...     manager_name: Mapped[str]
...     paperwork: Mapped[List["Paperwork"]] = relationship()
...     __mapper_args__ = {
...         "polymorphic_identity": "manager",
...     }
>>> class Paperwork(Base):
...     __tablename__ = "paperwork"
...     id: Mapped[int] = mapped_column(primary_key=True)
...     manager_id: Mapped[int] = mapped_column(ForeignKey("manager.id"))
...     document_name: Mapped[str]
...
...     def __repr__(self):
...         return f"Paperwork({self.document_name!r})"
>>>
>>> class Engineer(Employee):
...     __tablename__ = "engineer"
...     id: Mapped[int] = mapped_column(ForeignKey("employee.id"), primary_key=True)
...     engineer_info: Mapped[str]
...     __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(
...     Company(
...         name="Krusty Krab",
...         employees=[
...             Manager(
...                 name="Mr. Krabs",
...                 manager_name="Eugene H. Krabs",
...                 paperwork=[
...                     Paperwork(document_name="Secret Recipes"),
...                     Paperwork(document_name="Krabby Patty Orders"),
...                 ],
...             ),
...             Engineer(name="SpongeBob", engineer_info="Krabby Patty Master"),
...             Engineer(
...                 name="Squidward",
...                 engineer_info="Senior Customer Engagement Engineer",
...             ),
...         ],
...     )
... )
>>> session.commit()
BEGIN ...