Django用相关表上的条件注释总和答案

【问题标题】：Django annotate sum with a condition on a related tableDjango用相关表上的条件注释总和
【发布时间】：2013-03-21 03:45:37
【问题描述】：

class Inventory(models.Model):
    ...
    product = models.ForeignKey('Product')
    quantity = models.IntegerField(default=0)


class Order(models.Model):
    ...
    quantity = models.IntegerField()
    inventory = models.ForeignKey('Inventory')
    active = models.BooleanField(default=True)

# Not considering the orders that are not active
queryset = Inventory.objects.annotate(
    used=Sum('order__quantity')
).filter(product=product)

我需要获取带有注释“已使用”值的库存查询集。 'used' 值由所有相关但处于活动状态的订单的数量决定。

编辑：更准确地说，我只需要对活跃订单的数量求和。

【问题讨论】：

标签： sql django orm annotate

【解决方案1】：

queryset = Inventory.objects.filter(product=product, 
    order__active=True).aggregate(
    Sum('order__quantity'))

sum = queryset['order__quantity__sum']

【讨论】：

这会过滤订单仅处于活动状态的库存。也许我的问题不清楚。对此感到抱歉。我正在寻找的是所有“order_quantity”活动订单的总和。就像在总和中嵌套一个过滤器一样。
这就是您所需要的，对吧？ I need to get queryset of inventory that has annotated 'used' value. 'used' value is determined by quantity of all related orders but are active.
好的更新，sum of all 'order_quantity' for orders that are active
我需要对总和进行注释。在原始 SQL 中，它可能是这样的：SUM(CASE WHEN "order_invoiceline"."active" = 1 THEN "orders_invoiceline"."quantity" ELSE 0 END)

【解决方案2】：

我用原始 SQL 找到了答案：

SELECT "products_inventory"."id", "products_inventory"."product_id", "products_inventory"."quantity",
SUM(CASE WHEN "orders_order"."active" = True THEN "orders_order"."quantity" ELSE 0 END)
AS "used" FROM "products_inventory"
LEFT OUTER JOIN "orders_order" ON ("products_inventory"."id" = "orders_order"."inventory_id")
WHERE "products_inventory"."product_id" = id_of_product
GROUP BY "products_inventory"."id", "products_inventory"."product_id", "products_inventory"."quantity",
ORDER BY "products_inventory"."id" ASC

【讨论】：