在使用內部聯接和外部聯接創建查詢時遇到問題

Question

我有以下模型（簡化）：

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')

我想查詢某個父母的所有關系，我還想查詢某個用戶對這些關系所做的投票。 我嘗試過的：

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()

以及：

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()

當我執行這些查詢時，我得到空值。 我究竟做錯了什么？

Answer 1

只需打開SQL日志記錄（ echo=True ），您將看到第一個選項的結果SQL查詢類似於：

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

如果檢查它，您會注意到，子句vote.rel_id = relationship.id是JOIN子句和WHERE子句的一部分，這使得查詢過濾掉那些請求用戶沒有任何投票的Relationship行。

解：

1. 刪除冗余filter(Vote.rel_id == Relationship.id). 部分來自查詢。
2. 編輯1 ：同樣移動（刪除）用戶filter(Vote.voter_id == thisuser.id)從WHERE到LEFT JOIN子句： outerjoin(Vote, and_(Relationship.id == Vote.rel_id, Vote.voter_id == thisuser.id)) 。