我有两个表,并且已经定义了一对多的关系。
from sqlalchemy import Column, Integer, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
Base = declarative_base()
class Parent(Base):
__tablename__ = 'parent'
id = Column(Integer, primary_key=True)
children = relationship("Child", backref="parent")
class Child(Base):
__tablename__ = 'child'
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey('parent.id'))
如果我尝试访问Child.parent,我会收到错误消息。 但是,如果我初始化一个子实例,则错误消失。
我想初始化一个Child实例修改过的Child类,但我不明白怎么做。 如何在不创建Child实例的情况下访问Child.parent?
In [1]: Child.parent
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-2-8b757eeb36c4> in <module>()
----> 1 Child.parent
AttributeError: type object 'Child' has no attribute 'parent'
In [2]: Child()
Out[2]: <etl.es_utils.test_to_rm.Child at 0x7f38caf42c50>
In [3]: Child.parent
答案 0 :(得分:0)
我不是使用backref,而是定义两边的关系,它解决了这个问题。
from sqlalchemy import Column, Integer, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
Base = declarative_base()
class Parent(Base):
__tablename__ = 'parent'
id = Column(Integer, primary_key=True)
children = relationship("Child")
class Child(Base):
__tablename__ = 'child'
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey('parent.id'))
parent = relationship("Parent")