怎么写提前Django ORM查询

Question

To simplify things, lets say I have a models StockIOLog.

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

It contains following data:

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

type 0 means product was purchased, type 1 means product was consumed, Now I want to calculate total stock of every product batch-wise.

By running following SQL query

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

I get following queryset

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

How to do similar things in django ORM?

Answer 1

Maybe not the best answer, but You can get purchased and consumed in dictionary by following query

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())))
)