如何使用sqlalchemy中的关系更改父项？

Question

下面是与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') 
    ) 

需要从一个父到另一个重新分配一些孩子，则需要删除另一个父，但SQLAlchemy的父母删除之前删除的孩子......

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

p1.children.extend(p2.children) 
Session.delete(p2) 
Session.commit() 

登录：

... [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从另一父母分离...

Answer 1

唯一的解决方案我可以建议的是：

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

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

Session.delete(p2) 
Session.commit()