djangorestframework: Filtering in a related field

Question

Basically, I want to filter out inactive users from a related field of a ModelSerializer. I tried Dynamically limiting queryset of related field as well as the following:

class MySerializer(serializers.ModelSerializer):
  users = serializers.PrimaryKeyRelatedField(queryset=User.objects.filter(active=True), many=True)
  class Meta:
    model = MyModel
    fields = ('users',)

Neither of these approaches worked for just filtering the queryset. I want to do this for a nested related Serializer class as a field (but couldn't even get it to work with a RelatedField).

How do I filter queryset for nested relation?

Answer 1

I'll be curious to see a better solution as well. I've used a custom method in my serializer to do that. It's a bit more verbose but at least it's explicit.

Some pseudo code where a GarageSerializer would filter the nested relation of cars:

class MyGarageSerializer(...):
    users = serializers.SerializerMethodField('get_cars')

    def get_cars(self, garage):
        cars_queryset = Car.objects.all().filter(Q(garage=garage) | ...).select_related()
        serializer = CarSerializer(instance=cars_queryset, many=True, context=self.context)

        return serializer.data

Obviously replace the queryset with whatever you want. You don't always need the to give the context (I used it to retrieve some query parameters in the nested serializer) and you probably don't need the .select_related (that was an optimisation).

Answer 2

One way to do this is to create a method on the Model itself and reference it in the serializer:

#Models.py
class MyModel(models.Model):
    #...
    def my_filtered_field (self):
            return self.othermodel_set.filter(field_a = 'value_a').order_by('field_b')[:10]
#Serialziers.py
class MyModelSerialzer(serializers.ModelSerializer):
    my_filtered_field = OtherModelSerializer (many=True, read_only=True)
    class Meta:
        model   = MyModel
        fields  = [
            'my_filtered_field'             ,
            #Other fields ...
        ]