如何使用 sqlalchemy 中的关系更改父级？

Question

这里是与 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')
    )

需要从一个父级重新分配一些子级到另一个父级，然后需要删除另一个父级，但是 sqlalchemy 在删除父级之前删除了子级...

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......

Answer 1

我能建议的唯一解决方案是：

p1 = Session.query(Parent).get(...)
p2 = Session.query(Parent).get(...)

for child in p2.children[:]:
    child.parent = p1

Session.delete(p2)
Session.commit()