我与父母的关系如下。我希望能够区分空子级(例如,尚不知道的信息)与零子级。这是我目前正在采用的方法。它有效,但似乎有点麻烦。有没有更好的方法可以解决这个问题?
from sqlalchemy import Column, Integer, ForeignKey, create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
Base = declarative_base()
engine = create_engine('sqlite:///')
class Parent(Base):
__tablename__ = 'parent'
id = Column(Integer, primary_key=True)
children = relationship('Child', uselist=False)
class Child(Base):
__tablename__ = 'child'
id = Column(Integer, ForeignKey('parent.id'), primary_key=True)
child_items = relationship('ChildItem')
class ChildItem(Base):
__tablename__ = 'childitems'
id = Column(Integer, ForeignKey('child.id'), primary_key=True)
Base.metadata.create_all(engine)
p = Parent()
assert(p.children is None) # Would like to be able to do something like this.
c = Child()
c.child_items.append(ChildItem())
p.children = c
assert(p.children is not None)