如何编写高级 Django ORM 查询答案

【问题标题】：How write advance Django ORM query如何编写高级 Django ORM 查询
【发布时间】：2017-12-22 01:13:39
【问题描述】：

为了简化事情，假设我有一个模型 StockIOLog。

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

它包含以下数据：

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

type 0 表示产品已购买，type 1 表示产品已消耗，现在我想分批计算每个产品的总库存。

通过运行以下 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

我得到以下查询集

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

django ORM中如何做类似的事情？

【问题讨论】：

SQL查询的问题很难理解。你能解释一下这个场景吗？
@Md.Al-Amin 更简要地更新了问题

标签： python sql postgresql django-models django-rest-framework

【解决方案1】：

也许不是最好的答案，但您可以通过以下查询在字典中获取 purchased 和 consumed

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())))
)

【讨论】：