創建與內部查詢有問題加入與外連接

Question

我有以下的模型（簡體）：

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') 

我想查詢有一定的母公司所有的關係，我也想查詢票由某個用戶在這些關係上創建的。我試過什麼：

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() 

還有：

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() 

我得到空當我做這兩種查詢。我究竟做錯了什麼？

Answer 1

只需打開SQL日誌（echo=True），你會看到，第一個選項生成的SQL查詢是這樣的：

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 

如果你檢查它，你會發現該條款vote.rel_id = relationship.id是部分的JOIN子句和WHERE子句，這使查詢過濾掉那些沒有被請求的用戶投票的那些Relationship行。

解決方案：

1. 刪除冗餘filter(Vote.rel_id == Relationship.id).部分從查詢。
2. 編輯-1：也移動（刪除）的過濾器爲用戶filter(Vote.voter_id == thisuser.id)出WHERE並進入LEFT JOIN子句：outerjoin(Vote, and_(Relationship.id == Vote.rel_id, Vote.voter_id == thisuser.id))。