SQLAlchemy 在预加载时仅加载集合，而不加载 backref
例如（eagerload/joinedload 做同样的事情）：
session = Session()
parents = session.query(Parent).options(joinedload(Parent.children)).all()
session.close()
print parents[0].children # This works
print parents[0].children[0].parent # This gives a lazy loading error
在关闭会话之前添加以下循环有效（并且不会影响数据库）：
for p in parents:
for c in p.children:
c.parent
这非常愚蠢。有没有办法改变原始查询，以便加载关系的两侧，而无需在输出 SQL 中添加更多联接？
更新如果相关的话；这是映射
class Parent(Entity):
__tablename__ = "parent"
id = Column(Integer, primary_key=True)
children = relation("Child", backref="parent")
class Child(Entity):
__tablename__ = "child"
id = Column(Integer, primary_key=True)
parentId = Column(Integer, ForeignKey("parent.id"), index=True)
For example (eagerload/joinedload do the same thing):
session = Session()
parents = session.query(Parent).options(joinedload(Parent.children)).all()
session.close()
print parents[0].children # This works
print parents[0].children[0].parent # This gives a lazy loading error
Adding the following loop before closing the session works (and doesn't hit the DB):
for p in parents:
for c in p.children:
c.parent
Which is pretty dumb. Is there a way to alter the original query so that it loads both sides of the relation without adding more joins in the output SQL?
update In case it's relevant; here's the mapping
class Parent(Entity):
__tablename__ = "parent"
id = Column(Integer, primary_key=True)
children = relation("Child", backref="parent")
class Child(Entity):
__tablename__ = "child"
id = Column(Integer, primary_key=True)
parentId = Column(Integer, ForeignKey("parent.id"), index=True)
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这就是
contains_eager()< /a> 选项用于。请尝试以下操作：That's what
contains_eager()option is for. Try the following: