为 django 编写 FOR 循环的有效查询？

Question

我需要从这些模型中获取每个月购买的保单数量

class Insurance(models.Model):
  #other fields..
  date_purchased_on = models.DateField(auto_now_add=True)    
  customer_region = models.CharField(
    max_length=10, choices=RegionType.choices)

所以我写了一个观点来得到回复

@api_view(['GET'])
def chart_data(request):
    # structure of the op should be all the months from 1 to 12
    #  [{"month": 1,"count": 100,}, { "month:2", "count":20}]

    filtered_data = []
    for i in range(1, 13):
        query = Insurance.objects.filter(date_purchased_on__month=i).count()
        data = {
            "month": i,
            "count": query
        }
        filtered_data.append(data)
        
    return Response(filtered_data)

现在的问题是这个查询每次都会访问数据库大概有12次。有没有办法处理这个问题以进入 单个查询或减少它

和我的记录器结果

(0.000) SELECT COUNT(*) AS "__count" FROM "insurance_insurance" WHERE EXTRACT('month' FROM "insurance_insurance"."date_purchased_on") = 1; args=(1,); alias=default
(0.000) SELECT COUNT(*) AS "__count" FROM "insurance_insurance" WHERE EXTRACT('month' FROM "insurance_insurance"."date_purchased_on") = 2; args=(2,); alias=default
(0.000) SELECT COUNT(*) AS "__count" FROM "insurance_insurance" WHERE EXTRACT('month' FROM "insurance_insurance"."date_purchased_on") = 3; args=(3,); alias=default
(0.000) SELECT COUNT(*) AS "__count" FROM "insurance_insurance" WHERE EXTRACT('month' FROM "insurance_insurance"."date_purchased_on") = 4; args=(4,); alias=default
(0.000) SELECT COUNT(*) AS "__count" FROM "insurance_insurance" WHERE EXTRACT('month' FROM "insurance_insurance"."date_purchased_on") = 5; args=(5,); alias=default
(0.000) SELECT COUNT(*) AS "__count" FROM "insurance_insurance" WHERE EXTRACT('month' FROM "insurance_insurance"."date_purchased_on") = 6; args=(6,); alias=default
(0.000) SELECT COUNT(*) AS "__count" FROM "insurance_insurance" WHERE EXTRACT('month' FROM "insurance_insurance"."date_purchased_on") = 7; args=(7,); alias=default
(0.000) SELECT COUNT(*) AS "__count" FROM "insurance_insurance" WHERE EXTRACT('month' FROM "insurance_insurance"."date_purchased_on") = 8; args=(8,); alias=default
(0.000) SELECT COUNT(*) AS "__count" FROM "insurance_insurance" WHERE EXTRACT('month' FROM "insurance_insurance"."date_purchased_on") = 9; args=(9,); alias=default
(0.000) SELECT COUNT(*) AS "__count" FROM "insurance_insurance" WHERE EXTRACT('month' FROM "insurance_insurance"."date_purchased_on") = 10; args=(10,); alias=default
(0.000) SELECT COUNT(*) AS "__count" FROM "insurance_insurance" WHERE EXTRACT('month' FROM "insurance_insurance"."date_purchased_on") = 11; args=(11,); alias=default
(0.000) SELECT COUNT(*) AS "__count" FROM "insurance_insurance" WHERE EXTRACT('month' FROM "insurance_insurance"."date_purchased_on") = 12; args=(12,); alias=default

Answer 1

您可以使用

ExtractMonth

表达式提取月份并按该月排序 ^[Django-doc]:

from django.db.models import Count
from django.db.models.functions import ExtractMonth

Insurance.objects.values(month=ExtractMonth('date_purchased_on')).annotate(
    count=Count('pk')
).order_by('month')

这将产生一个

QuerySet

的字典，如下所示：

<QuerySet [
    {'month': 6, 'count': 100 },
    {'month': 7, 'count': 20 }
]>

没有

Insurance

对象的月份将 not 包含在

QuerySet

中。因此，您可能必须对其进行后处理，并包含带有

'count': 0

的记录。