SQLAlchemy的多表連接

Question

我試圖做SQLAlchemy的

select * from splits s 
join transactions t on t.guid = s.tx_guid 
join accounts a on a.guid = s.account_guid 
left join splits s2 on s2.tx_guid = t.guid 
join accounts a2 on a2.guid = s2.account_guid 
where a.name = 'Checking Account' and t.post_date > '2012-02-29' 
order by t.post_date desc 

以下連接使用這些模型

class Account(db.Model): 
    __table__ = db.Table('accounts', db.metadata, autoload=True, autoload_with=db.engine) 
    splits = db.relationship('Split', backref='account') 

class Transaction(db.Model): 
    __table__ = db.Table('transactions', db.metadata, autoload=True, autoload_with=db.engine) 
    splits = db.relationship('Split', backref='transaction') 

class Split(db.Model): 
    __table__ = db.Table('splits', db.metadata, 
          db.Column('tx_guid', db.VARCHAR, db.ForeignKey('transactions.guid')), 
          db.Column('account_guid', db.VARCHAR, db.ForeignKey('accounts.guid')), 
          autoload=True, autoload_with=db.engine) 

我得到儘可能這個，但現在我被困

q = Split.query.join(Transaction). \ 
       join(Account). \ 
       options(db.joinedload(Split.transaction)). \ 
       options(db.joinedload(Split.account)). \ 
       filter(Account.name == 'Checking Account'). \ 
       filter(Transaction.post_date > date(2012, 02, 29)). \ 
       order_by(db.desc(Transaction.post_date)) 

我該如何離開加入交易與分裂然後那些將與帳戶分開，即上面兩個查詢的最後兩個連接？

Answer 1

當你想指的是同一個表中多次查詢，則需要使用aliased()結構：

s = db.aliased(Split) 
a = db.aliased(Account) 
q = db.session.query(Split).\ 
    options(joinedload(Split.transaction)).\ 
    options(joinedload(Split.account)).\ 
    join(Transaction).\ 
    join(Account).\ 
    outerjoin(s, Transaction.splits).\ 
    join(a, a.guid == s.account_guid).\ 
    filter(Account.name == 'Checking Account').\ 
    filter(Transaction.post_date > date(2012, 2, 29)).\ 
    order_by(Transaction.post_date.desc()) 

而且be careful when mixing INNER and OUTER joins。