如何将SQL语句转换为正确的SQLAlchemy表达式

Question

我有一条SQL语句来计算我在不同项目上拥有的库存量。 因此，我总结了所有已交付的物品并减去了已售出的所有物品。 给我正确结果的SQL语句如下：

SELECT     Item.id,
    Item.description,
    deliver.del_amount,
    sell.sell_amount ,
    deliver.del_amount - sell.sell_amount as stock
from item
join (
    select Deliveryitem.Item_id as del_id,
    sum(DeliveryItem.amount) as del_amount
    from  Deliveryitem group by DeliveryItem.item_id

) deliver on deliver.del_id = item.id
 join (
    SELECT LineItem.Item_id as sell_id,
    sum(LineItem.amount) as sell_amount
    from  LineItem  group by LineItem.item_id
) sell on sell.sell_id=item.id

现在，我需要将其转换为等效的SQLAlchemy语句。 我不知道如何结合交付和销售标签正确地表达两个联接。 有人可以帮我吗？

Answer 1

SQLAlchemy的优点在于，当您开始使用SQLAlchemy表达式语法难以表达的复杂查询时，可以使用直接SQL并将结果填充到ORM类中。

您可以按照以下方式做一些事情

Session.query(Item, deliver, sell, stock).from_statement("""
SELECT     Item.id,
    Item.description,
    deliver.del_amount,
    sell.sell_amount ,
    deliver.del_amount - sell.sell_amount as stock
from item
join (
    select Deliveryitem.Item_id as del_id,
    sum(DeliveryItem.amount) as del_amount
    from  Deliveryitem group by DeliveryItem.item_id

) deliver on deliver.del_id = item.id
 join (
    SELECT LineItem.Item_id as sell_id,
    sum(LineItem.amount) as sell_amount
    from  LineItem  group by LineItem.item_id
) sell on sell.sell_id=item.id
""")