怎么写先进的Django ORM查询

为了简化事情，可以说我有一个模型StockIOLog。怎么写先进的Django ORM查询

class StockIOLog(models.Model): 
    pid = models.IntegerField() 
    name= models.CharField(max_length=50) 
    type= models.IntegerField() 
    stock = models.IntegerField()

它包含了以下数据：

pid | name | batch | type | quantity 
------------------------------------------------ 
1 | Napa | AB | 0  | 100 
------------------------------------------------ 
1 | Napa | AA | 0  | 100 
------------------------------------------------ 
2 | Amod | AA | 0  | 100 
------------------------------------------------ 
2 | Amod | CA | 0  | 100 
------------------------------------------------ 
1 | Napa | AB | 1  | 10 
------------------------------------------------ 
1 | Napa | AB | 1  | 5 
------------------------------------------------ 
1 | Napa | AA | 1  | 20 
------------------------------------------------ 
2 | Amod | AA | 1  | 10 
------------------------------------------------ 
2 | Amod | AA | 1  | 50 
------------------------------------------------ 
2 | Amod | CA | 1  | 5 
------------------------------------------------ 
2 | Amod | CA | 1  | 15

类型0意味着购买产品，1型是指产品的被消耗，现在我想计算分批每一个产品的库存总量。

通过运行下面的SQL查询

SELECT pid, name, batch, SUM(in) - SUM(out) as stock FROM (
    SELECT pid, name, type SUM(quantity) as in, 0 as out from `qset` WHERE type=0 GROUP BY pid,type,batch as a 
    UNION 
    SELECT pid, name, type 0 as in, SUM(quantity) as out from `qset` WHERE type=1 GROUP BY pid,type,batch as b 
) ac table_a

我获得以下查询集

pid | name | batch | stock 
----------------------------------- 
1 | Napa | AB | 85 
----------------------------------- 
1 | Napa | AA | 80 
----------------------------------- 
2 | Amod | AA | 40 
----------------------------------- 
2 | Amod | CA | 80

如何做类似的事情在Django ORM？

来源

2017-07-17 Ashraful Alam

得到字典purchased和consumed这是很难理解的SQL查询的问题。你能解释一下这个场景吗？ –

@ Md.Al-Amin更简短地更新了问题 –

也许不是最好的答案，但你可以通过下面的查询

from django.db.models import When, F, IntegerField, Sum, Count 
from .models import StockIOLog 

values = (StockIOLog.objects.all().values("pid", "name", "batch").annotate(
    purchased=Sum(Case(When(type=1, then=F("stock")), 
         output_filed=IntegerField())), 
    consumed=Sum(Case(When(type=0, then=F("stock")), 
         output_field=IntegerField()))) 
)

来源

2017-07-21 09:53:08 safwan

怎么写先进的Django ORM查询

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