django用动态列名注释 [英] django annotate with dynamic column name

问题描述

我在Django应用中有一个模型，其结构如下：

I have a model in django app, with the following structure:

class items(models.Model):
    name = models.CharField(max_length=50)
    location = models.CharField(max_length=3)

我想为每个名称/项目的每个位置的计数创建一个数据透视表，我设法按照以下步骤进行操作：

I wanted to create a pivot table for the count of each location per each name/item, which I managed to do as per the following:

queryset_res = items.objects.values('name')\
                            .annotate(NYC=Sum(Case(When(location='NYC', then=1),default=Value('0'),output_field=IntegerField())))\
                            .annotate(LND=Sum(Case(When(location='LND', then=1),default=Value('0'),output_field=IntegerField())))\
                            .annotate(ASM=Sum(Case(When(location='ASM', then=1),default=Value('0'),output_field=IntegerField())))\
                            .annotate(Total=Count('location'))\
                            .values('name', 'NYC', 'LSA','Total')\
                            .order_by('-Total')

这给了我多少

我的问题是如何使位置动态化，所以如果添加了新位置，我就没有了回来并再次更改代码！来自列表或来自模型数据本身

my question is how can I make the location dynamic, and so if new locations where added I don't have come back and change the code again! either from a list or from the model data itself

非常感谢
AB

Many Thanks AB

推荐答案

您可以将动态参数与 * [1、2、3] ， ** {'key'：'value '} 在python中。

You can bind dynamic parameter with *[1, 2, 3], **{'key': 'value'} in python.

from django.db.models import Case, Count, Sum, IntegerField, Value, When

def get_annotation(key):
    return {
        key: Sum(
            Case(
                When(location=key, then=Value(1)),
                default=Value(0),
                output_field=IntegerField(),
           ),
        ),
    }

queryset_res = items.objects.values('name')
location_list = ['NYC', 'LSA', 'ASM', ...etc]
for key in location_list:
    queryset_res = queryset_res.annotate(**get_annotation(key))
    
queryset_res = (
    queryset_res.annotate(Total=Count("location"))
    .values("name", "Total", *location_list)
    .order_by("-Total")
)

现在，您只需更改以下内容即可实现一组查询 location_list 。

Now you can implement a set of queries simply by changing location_list.

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