Django 模型 Count 和 Q 方法抛出类型错误

Question

我正在尝试根据用户输入值生成动态查询。正常的查询是这样的：

result = (
    my_model
    .objects
    .aggregate(
        Type1=Count(
            'pk',
            filter=Q(db_field=1)),
        Type2=Count(
            'pk', 
            filter=Q(db_field=2)),
        Type3=Count(
            'pk',
            filter=Q(db_field=3)),
        Type4=Count(
            'pk', 
            filter=Q(db_field=4)),
        Type5=Count(
            'pk', 
            filter=Q(db_field=5)))

这是我为测试编写的代码：

from django.db.models import (Count, Q)

field = field_values # (it's tuple and read from input)
aggregate_query = ''
if field != None:
   for j in field:
   aggregate_query += f"{j[1]}={Count}('pk', filter={Q}(db_field={j[0]})),"

my_model.objects.aggregate(aggregate_query[:-1])

当我在 python 控制台上评估时，聚合查询正确生成并得到结果，但是当我执行此代码时，它抛出以下错误：

QuerySet.aggregate() received non-expression(s): 
Type1=<class 'django.db.models.aggregates.Count'>('pk', filter=<class 'django.db.models.query_utils.Q'>(db_field=1)),
Type2=<class 'django.db.models.aggregates.Count'>('pk', filter=<class 'django.db.models.query_utils.Q'>(db_field=2)),
Type3=<class 'django.db.models.aggregates.Count'>('pk', filter=<class 'django.db.models.query_utils.Q'>(db_field=3)),
Type4=<class 'django.db.models.aggregates.Count'>('pk', filter=<class 'django.db.models.query_utils.Q'>(db_field=4)),
Type5=<class 'django.db.models.aggregates.Count'>('pk', filter=<class 'django.db.models.query_utils.Q'>(db_field=5)).

有人可以帮我解决这个问题吗？

Answer 1

问题是f"{j[1]}={Count}('pk', filter={Q}(db_field={j[0]})),"是一个字符串，不能用字符串查询。

你可以构造一个带有推导式的字典，然后将其用于查询：

from django.db.models import (Count, Q)

field = field_values
aggregate_query = {j[1]: Count('pk', filter=Q(db_field=j[0])) for j in field} if j != None else {}
my_model.objects.aggregate(**aggregate_query)

Django 模型 Count 和 Q 方法抛出类型错误

Django models Count and Q methods are throwing type error

django

postgresql

django-models

django-rest-framework

graphene-django