python - 为什么 SQLAlchemy 不使用 SQLite 强制执行外键约束？

Question

我对 SqlAlchemy 外键约束有一些误解。我的理解是，下面插入 B 应该引发ForeignKeyConstraint 异常，因为没有 A 以 "my_a" 作为名称。这不是外键约束的作用吗？更新约束表时要求约束映射的表列中存在值？

from sqlalchemy import Column, create_engine, ForeignKey, Integer, VARCHAR
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

Base = declarative_base()


class A(Base):
    __tablename__ = 'table_A'
    id = Column(Integer, primary_key=True)
    name = Column(VARCHAR(32))


class B(Base):
    __tablename__ = 'table_B'
    id = Column(Integer, primary_key=True)
    a_name = Column(VARCHAR(32), ForeignKey('table_A.name'), nullable=False)


engine = create_engine('sqlite:////tmp/AB.db.foo')
Base.metadata.create_all(engine)

Session = sessionmaker()
Session.configure(bind=engine)

b = B(a_name="my_a")

session = Session()
session.add(b)
session.commit()
session.close()

Answer 1

SQLite – 即使是现代版本 – 默认情况下不强制执行外键。

Assuming the [SQLite] library is compiled with foreign key constraints enabled, it must still be enabled by the application at runtime, using the PRAGMA foreign_keys command.

SQLite documentation

SQLAlchemy documentation