这是与 backref 和删除级联关系的简单示例。
class Parent(Base):
__tablename__ = 'parent'
id = Column(Integer, primary_key=True)
class Child(Base):
__tablename__ = 'child'
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey('Parent.id'))
parent = relation(
'Parent',
backref=backref('children', cascade='delete, delete-orphan')
)
需要将一些孩子从一个父母重新分配给另一个父母,然后需要删除另一个父母,但是 sqlalchemy 在删除父母之前会删除孩子......
p1 = Session.query(Parent).get(...)
p2 = Session.query(Parent).get(...)
p1.children.extend(p2.children)
Session.delete(p2)
Session.commit()
日志:
... [worker 0] UPDATE child SET parent_id=%(parent_id)s WHERE child.id = %(child_id)s
...
... [worker 0] DELETE FROM child WHERE child.id = %(id)s
...
... [worker 0] DELETE FROM parent WHERE parent.id = %(id)s
...
... [worker 0] COMMIT
需要以某种方式将孩子与另一个父母分开......