创建与内部查询有问题加入与外连接

Question

我有以下的模型（简体）：

class User(Base): 
    __tablename__ = 'user' 
    id = Column(Integer, primary_key=True) 

class Thing(Base): 
    __tablename__ = 'thing' 
    id = Column(Integer, primary_key=True) 

class Relationship(Base): 
    __tablename__ = 'relationship' 
    id = Column(Integer, primary_key=True) 
    parent_id = Column(Integer, ForeignKey('thing.id')) 
    parent = relationship('Thing', backref='parentrelationships', primaryjoin = "Relationship.parent_id == Thing.id") 
    child_id = Column(Integer, ForeignKey('thing.id')) 
    child = relationship('Thing', backref='childrelationships', primaryjoin = "Relationship.child_id == Thing.id") 

class Vote(Base) 
    __tablename__ = 'vote' 
    id = Column(Integer, primary_key=True) 
    rel_id = Column(Integer, ForeignKey('relationship.id')) 
    rel = relationship('Relationship', backref='votes') 
    voter_id = Column(Integer, ForeignKey('user.id')) 
    voter = relationship('User', backref='votes') 

我想查询有一定的母公司所有的关系，我也想查询票由某个用户在这些关系上创建的。我试过什么：

def get_relationships(thisthing, thisuser): 
    return DBSession.query(Relationship, Vote).\ 
     filter(Relationship.parent_id == thisthing.id).\ 
     outerjoin(Vote, Relationship.id == Vote.rel_id).\ 
     filter(Vote.voter_id == thisuser.id).\ 
     filter(Vote.rel_id == Relationship.id).\ 
     all() 

还有：

def get_relationships(thisthing, thisuser): 
    session = DBSession() 
    rels = session.query(Relationship).\ 
     filter(Relationship.parent_id == thisthing.id).\ 
     subquery() 
    return session.query(rels, Vote).\ 
     outerjoin(Vote, rels.c.id == Vote.rel_id).\ 
     filter(Vote.voter_id == thisuser.id).\ 
     all() 

我得到空当我做这两种查询。我究竟做错了什么？

Answer 1

只需打开SQL日志（echo=True），你会看到，第一个选项生成的SQL查询是这样的：

SELECT relationship.id AS relationship_id, relationship.parent_id AS relationship_parent_id, relationship.child_id AS relationship_child_id, vote.id AS vote_id, vote.rel_id AS vote_rel_id, vote.voter_id AS vote_voter_id 
FROM relationship LEFT OUTER JOIN vote ON relationship.id = vote.rel_id 
WHERE relationship.parent_id = ? AND vote.voter_id = ? AND vote.rel_id = relationship.id 

如果你检查它，你会发现该条款vote.rel_id = relationship.id是部分的JOIN子句和WHERE子句，这使查询过滤掉那些没有被请求的用户投票的那些Relationship行。

解决方案：

1. 删除冗余filter(Vote.rel_id == Relationship.id).部分从查询。
2. 编辑-1：也移动（删除）的过滤器为用户filter(Vote.voter_id == thisuser.id)出WHERE并进入LEFT JOIN子句：outerjoin(Vote, and_(Relationship.id == Vote.rel_id, Vote.voter_id == thisuser.id))。