How to count foreign key objects with annotation in Django? - python-3.x

Question

Hi all!
New in Django, and confused, help is appreciated!
Have three models:
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)
Objects of Organization model:
organization_name
Organization 1
Organization 2
Objects of AppealForm model:
form_name
In written form
In oral form
Objects of Appeal model:
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
I'm trying to create a table in the template, like:
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
The content in the table contents has to be retrieved from Appeal model, that is rendered to the template.
Question:
How the query look like in views.py using Appeal model?

Answer 1

i recommend you read about how to do complex query in django from this documents section.
Here what your query would be like:
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()
set the above query to a value and loop through it and see the results. You should get something like this
[{'organization': 'Organization 1', 'total_appeals': 3,
'written_amount': 1, 'oral_amount': 2}, {'organization':
'Organization 2', 'total_appeals': 2, 'written_amount': 1,
'oral_amount': 1}]
Explanations:
values to group by organization
Count to count the form in that organization group
we use Case to add an if condition, then=1 to return value(else return null)
the written_amount need to be integer so we set it in the output_field
conditional part in the documents https://docs.djangoproject.com/en/dev/ref/models/conditional-expressions
why you should use order_by() for grouping queries https://docs.djangoproject.com/en/4.0/topics/db/aggregation/#interaction-with-order-by