我稍微修改了一下官方的example for a directed graph如果在子级中定义了关系,则按照级联删除的建议添加 cascade='all, delete-orphan
。不过,当我尝试删除父级时,我收到了外键约束错误。
我希望能够删除一个 Node 对象,并且所有相关的 Edge 也应该被删除。首选使用passive_deletes=True,但我也没有让它工作。
经过我修改的完整源代码,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()
最佳答案
删除是通过 session.query().delete() 完成的,它不适用于 SQLAlchemy 级联,需要在数据库中级联才能工作。
关于python - 使用SQLAlchemy删除级联外键约束错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/49502579/