ORM 查询指南设置：列加载

本页说明了 列加载选项 文档中使用的映射和固定数据 ORM 查询指南.

>>> from typing import List
>>> from typing import Optional
>>>
>>> from sqlalchemy import Column
>>> from sqlalchemy import create_engine
>>> from sqlalchemy import ForeignKey
>>> from sqlalchemy import LargeBinary
>>> from sqlalchemy import Table
>>> from sqlalchemy import Text
>>> 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 User(Base):
...     __tablename__ = "user_account"
...     id: Mapped[int] = mapped_column(primary_key=True)
...     name: Mapped[str]
...     fullname: Mapped[Optional[str]]
...     books: Mapped[List["Book"]] = relationship(back_populates="owner")
...
...     def __repr__(self) -> str:
...         return f"User(id={self.id!r}, name={self.name!r}, fullname={self.fullname!r})"
>>> class Book(Base):
...     __tablename__ = "book"
...     id: Mapped[int] = mapped_column(primary_key=True)
...     owner_id: Mapped[int] = mapped_column(ForeignKey("user_account.id"))
...     title: Mapped[str]
...     summary: Mapped[str] = mapped_column(Text)
...     cover_photo: Mapped[bytes] = mapped_column(LargeBinary)
...     owner: Mapped["User"] = relationship(back_populates="books")
...
...     def __repr__(self) -> str:
...         return f"Book(id={self.id!r}, title={self.title!r})"
>>> engine = create_engine("sqlite+pysqlite:///:memory:", echo=True)
>>> Base.metadata.create_all(engine)
BEGIN ...
>>> conn = engine.connect()
>>> session = Session(conn)
>>> session.add_all(
...     [
...         User(
...             name="spongebob",
...             fullname="Spongebob Squarepants",
...             books=[
...                 Book(
...                     title="100 Years of Krabby Patties",
...                     summary="some long summary",
...                     cover_photo=b"binary_image_data",
...                 ),
...                 Book(
...                     title="Sea Catch 22",
...                     summary="another long summary",
...                     cover_photo=b"binary_image_data",
...                 ),
...                 Book(
...                     title="The Sea Grapes of Wrath",
...                     summary="yet another summary",
...                     cover_photo=b"binary_image_data",
...                 ),
...             ],
...         ),
...         User(
...             name="sandy",
...             fullname="Sandy Cheeks",
...             books=[
...                 Book(
...                     title="A Nut Like No Other",
...                     summary="some long summary",
...                     cover_photo=b"binary_image_data",
...                 ),
...                 Book(
...                     title="Geodesic Domes: A Retrospective",
...                     summary="another long summary",
...                     cover_photo=b"binary_image_data",
...                 ),
...                 Book(
...                     title="Rocketry for Squirrels",
...                     summary="yet another summary",
...                     cover_photo=b"binary_image_data",
...                 ),
...             ],
...         ),
...     ]
... )
>>> session.commit()
BEGIN ... COMMIT
>>> session.close()
>>> conn.begin()
BEGIN ...