[英]Delete cascade foreign key constraint error with SQLAlchemy
I slightly modified the official example for a directed graph and added a cascade='all, delete-orphan
as recommended for cascading deletion if the relationship is defined in the child. 我稍微修改了有向图的官方示例,并建议如果级联关系在子级中定义,则建议
cascade='all, delete-orphan
级联删除。 Still, when I try to delete a parent I get a foreign key constraint error. 但是,当我尝试删除父母时,仍然收到外键约束错误。
I want to be able to delete a Node object and all related Edges should also be deleted. 我希望能够删除Node对象,并且所有相关的Edge也应该删除。 Using passive_deletes=True would be preferred, I did not get that to work either.
最好使用passive_deletes = True,我也没有使它正常工作。
Full sourcecode with my modifications, removed mysql connection data: 经过我的修改的完整源代码,删除了mysql连接数据:
"""a directed graph example."""
from sqlalchemy import Column, Integer, ForeignKey, \
create_engine
from sqlalchemy.orm import relationship, sessionmaker, backref
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Node(Base):
__tablename__ = 'node'
node_id = Column(Integer, primary_key=True)
def higher_neighbors(self):
return [x.higher_node for x in self.lower_edges]
def lower_neighbors(self):
return [x.lower_node for x in self.higher_edges]
class Edge(Base):
__tablename__ = 'edge'
lower_id = Column(
Integer,
ForeignKey('node.node_id'),
primary_key=True)
higher_id = Column(
Integer,
ForeignKey('node.node_id'),
primary_key=True)
lower_node = relationship(
Node,
primaryjoin=lower_id == Node.node_id,
backref=backref('lower_edges', cascade='all, delete-orphan'))
higher_node = relationship(
Node,
primaryjoin=higher_id == Node.node_id,
backref=backref('higher_edges', cascade='all, delete-orphan'))
def __init__(self, n1, n2):
self.lower_node = n1
self.higher_node = n2
engine = create_engine('mysql+pymysql:', echo=True)
Base.metadata.drop_all(engine)
Base.metadata.create_all(engine)
session = sessionmaker(engine)()
# create a directed graph like this:
# n1 -> n2 -> n1
# -> n5
# -> n7
# -> n3 -> n6
n1 = Node()
n2 = Node()
n3 = Node()
n4 = Node()
n5 = Node()
n6 = Node()
n7 = Node()
Edge(n1, n2)
Edge(n1, n3)
Edge(n2, n1)
Edge(n2, n5)
Edge(n2, n7)
Edge(n3, n6)
session.add_all([n1, n2, n3, n4, n5, n6, n7])
session.commit()
session = sessionmaker(engine)()
session.query(Node).filter(Node.node_id==1).delete()
session.commit()
删除是通过session.query()。delete()完成的,该方法不适用于SQLAlchemy级联,需要在数据库中级联才能工作。
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