SQLAlchemy將外部聯接ORM查詢轉換為Core

Question

使用核心組件時，我遇到SQLAlchemy的 select_from語句問題。 我嘗試構建一個外連接查詢，目前看起來像：

 
 
 
 
  
  
  query = select([b1.c.id, b1.c.num, n1.c.name, n1.c.num, ...] ).where(and_( ... some conditions ... ) ).select_from( ???.outerjoin( n1, and_( ... some conditions ... ) ).select_from(... more outer joins similar to the above ...)
 
 
  

根據文檔，結構應如下所示：

 
 
 
 
  
  
  table1 = table('t1', column('a')) table2 = table('t2', column('b')) s = select([table1.ca]).\\ select_from( table1.join(table2, table1.ca==table2.cb) )
 
 
  

我的問題是在這種情況下我沒有table1對象，因為 select ...部分由列而不是單個表組成（請參閱我的查詢中的問號）。 我嘗試過使用 n1.outerjoin(n1... ，但是這會導致異常（ Exception: (ProgrammingError) table name "n1" specified more than once ）。

上面的代碼片段來自基於工作會話的（ORM）查詢，我試圖轉換（成功有限）。

ProgrammingError: (ProgrammingError) table name "customer1" specified more than once
 'SELECT customer1.id, customer.name, order1.id, order1.order_num, address1.id, address1.city \nFROM customer, customer AS customer1 LEFT OUTER JOIN "order" AS order1 ON order1.customer_id = customer1.id, customer AS customer1 LEFT OUTER JOIN address AS address1 ON customer1.id = address1.customer_id' {}

如何將此ORM查詢轉換為純Core查詢？ 更新：

我能夠縮小問題的范圍。 似乎兩個select_from調用的組合導致了問題。

 customer = Table('customer', metadata, Column('id', Integer), Column('name', String(50)), ) order = Table('order', metadata, Column('id', Integer), Column('customer_id', Integer), Column('order_num', Integer), ) address = Table('address', metadata, Column('id', Integer), Column('customer_id', Integer), Column('city', String(50)), ) metadata.create_all(db) customer1 = aliased(customer, name='customer1') order1 = aliased(order, name='order1') address1 = aliased(address, name='address1') columns = [ customer1.c.id, customer.c.name, order1.c.id, order1.c.order_num, address1.c.id, address1.c.city ] query = select(columns) query = query.select_from( customer1.outerjoin( order1, and_( order1.c.customer_id==customer1.c.id, ) ) ) query = query.select_from( customer1.outerjoin( address1, and_( customer1.c.id==address1.c.customer_id ) ) ) result = connection.execute(query) for r in result.fetchall(): print r 

上面的代碼導致以下異常：

 ProgrammingError: (ProgrammingError) table name "customer1" specified more than once 'SELECT customer1.id, customer.name, order1.id, order1.order_num, address1.id, address1.city \\nFROM customer, customer AS customer1 LEFT OUTER JOIN "order" AS order1 ON order1.customer_id = customer1.id, customer AS customer1 LEFT OUTER JOIN address AS address1 ON customer1.id = address1.customer_id' {} 

如果我在使用SQLAlchemy方面有一點經驗，我會說這可能是一個錯誤......

Answer 1

我終於設法解決了這個問題。 而不是級聯select_from ，需要將其他連接鏈接到實際連接。 上面的查詢將是：

query = select(columns)
query = query.select_from(
    customer1.outerjoin(
        order1,
        and_(
            order1.c.customer_id==customer1.c.id,
        )
    ).outerjoin(
        address1,
        and_(
            customer1.c.id==address1.c.customer_id
        )
    )
)