如何计算 Django 中带注释的外键对象？

Question

大家好！

Django 新手，困惑中，不胜感激！

拥有三个模型：

class Organization(models.Model):
    organization_name = models.CharField(max_length=50)


class AppealForm(models.Model):
    form_name = models.CharField(max_length=50)


class Appeal(models.Model):
    organization = models.ForeignKey(Organization, on_delete=models.CASCADE)
    appeal_form = models.ForeignKey(AppealForm, on_delete=models.CASCADE)
    applicant_name = models.CharField(max_length=150)

组织模型的对象：

organization_name
Organization 1
Organization 2

AppealForm 模型的对象：

form_name
In written form
In oral form

上诉对象模型：

organization	appeal_form	applicant_name
Organization 1	In written form	First and Last name
Organization 1	In oral form	First and Last name
Organization 1	In oral form	First and Last name
Organization 2	In written form	First and Last name
Organization 2	In oral form	First and Last name

我正在尝试在模板中创建一个 table，例如：

Organization	Total amount of appeals	Amount of written form appeals	Amount of oral form appeals
Organization 1	3	1	2
Organization 2	2	1	1

必须从上诉模型中检索 table 内容中的内容，然后呈现给模板。

问题： 使用上诉模型的 views.py 中的查询是什么样的？

Answer 1

我建议您从 documents 部分阅读有关如何在 Django 中执行复杂查询的信息。您的查询如下：

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

Appeal.objects
      .values('organization')
      .annotate(
          total_appeals=Count('appeal_form'), 
          written_amount=Count(Case(
                When(appeal_form__form_name="In written form", then=1),
                output_field=IntegerField(),
          )),
          oral_amount=Count(Case(
                When(appeal_form__form_name="In oral form", then=1),
                output_field=IntegerField(),
          )),
       ).order_by()

将上述查询设置为一个值并遍历它并查看结果。你应该得到这样的东西

[{'organization': 'Organization 1', 'total_appeals': 3, 'written_amount': 1, 'oral_amount': 2}, {'organization': 'Organization 2', 'total_appeals': 2, 'written_amount': 1, 'oral_amount': 1}]

解释：

要按 organization
Count 统计该组织组中的表格
我们使用 Case 添加一个 if condition，然后 =1 到 return 值（否则 return null）
written_amount 需要是整数所以我们在 output_field

文档中的条件部分https://docs.djangoproject.com/en/dev/ref/models/conditional-expressions

为什么应该使用 order_by() 来对查询进行分组 https://docs.djangoproject.com/en/4.0/topics/db/aggregation/#interaction-with-order-by

如何计算 Django 中带注释的外键对象？

How to count foreign key objects with annotation in Django?

python-3.x

django

django-models

django-views

django-templates