Django-REST-Framework "GroupBy" ModelSerializer - django

Question

I have the following situation
class MyModel(models.Model):
key = models.CharField(max_length=255)
value = models.TextField(max_length=255)
category = models.CharField(max_length=4)
mode = models.CharField(max_length=4)
the fields key, category and mode are unique together. I have the following objects:
m1 = MyModel(key='MODEL_KEY', value='1', category='CAT_1' mode='MODE_1')
m2 = MyModel(key='MODEL_KEY', value='2', category='CAT_1' mode='MODE_2')
m3 = MyModel(key='MODEL_KEY', value='1', category='CAT_2' mode='MODE_1')
m4 = MyModel(key='MODEL_KEY', value='2', category='CAT_2' mode='MODE_2')
I want to expose an API that will group by key and category so the serialized data will look something like this:
{
"key": "MODEL_KEY",
"category": "CAT_1"
"MODE_1": { "id": 1, "value": "1" }
"MODE_2": { "id": 2, "value": "2" }
},
{
"key": "MODEL_KEY",
"category": "CAT_2"
"MODE_1": { "id": 3, "value": "1" }
"MODE_2": { "id": 4, "value": "2" }
}
Is there any way of doing this in django rest framework with ModelSerializer.

Answer 1

There is module that allows you to group Django models and still work with a QuerySet in the result: https://github.com/kako-nawao/django-group-by
Using the above to form your queryset:
# Postgres specific!
from django.contrib.postgres.aggregates.general import ArrayAgg
qs = MyModel.objects.group_by('key', 'category').annotate(
mode_list=ArrayAgg('mode')).order_by(
'key', 'category').distinct()
You can then access the properties key, category and mode_list on the resulting QuerySet items as attributes like qs[0].mode_list. Therefore, in your serializer you can simply name them as fields.
The model_list field might require a SerializerMethodField with some custom code to transform the list.
Note that you need an aggregation if you don't want to group by mode, as well.