How to filter Django REST Framework queryset by foreign key of nested object?

Question

I have the following Django models:

class Pa(models.Model):
   pa_name = models.CharField

class Pb(models.Model):
    pa = models.ForeignKey(Pa, related_name="pbs")
    pb_name = models.CharField()

class Pc(models.Model):
    pb = models.ForeignKey(Pb, related_name="pcs")
    pc_name = models.CharField()

The queryset of Pc has this structure:

[
  { "id": 1,
    "pc_name": "pc_1",
    "pb" = {
      "id": 10,
      "pb_name": "pb_1",
      "pa" : {
        "pa_name" : "pa_1"  # <-- How to filter queryset by pa_name attribute?
      }
    }
  },
  { "id": 2,
    "pc_name": "pc_2",
    "pb" = {
      "id": 20,
      "pb_name": "pb_2",
      "pa" : {
        "pa_name" : "pa_2"
      }
    }
  },
  # ...
]

I'd like to return all those Pcs, where pa_name is "pa_1", i.e. filter over the 2. level nested object.

TMOTTM · Accepted Answer · 2021-07-11 21:15:56Z

2

Possible using a chained filter:

pcs = Pc.objects.filter(pb__pa__pa_name=pa_name)

answered Jul 11, 2021 at 21:15

TMOTTM

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Comments

Rahul Raj · Accepted Answer · 2021-07-12 07:49:13Z

You can write your own filter class then define what you want to filter:

import django_filters.rest_framework
import django_filters.filters

class FilterClass(django_filters.rest_framework.FilterSet):
    pb = django_filters.CharFilter(
        method="filter_pa", label="Pa filter"
    )
    class Meta:
        model = models.Pc
        fields = { 
            "pc_name": ["icontains"],
        }
    
    def filter_pb(self, queryset, field_name, value):
        return queryset.filter(
            pb__pb_name__icontains=value
        ).distinct()

class PC(APIView):
    filterset_class = FilterClass

So this filter set will allow you to filter your pb_name. Hope this answer will help you to solve your problem.

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