[Django]-Add a count field to a django rest framework serializer

by

52👍

✅

This should work

class GroupSerializer(serializers.ModelSerializer):

    user_count = serializers.SerializerMethodField()

    class Meta:
        model = Group
        fields = ('id', 'name','user_count')

    def get_user_count(self, obj):
        return obj.user_set.count()

This adds a user_count field to your serializer whose value is set by get_user_count, which will return the length of the user_set.

You can find more information on SerializerMethodField here: http://www.django-rest-framework.org/api-guide/fields/#serializermethodfield

👤emre.

79👍

A bit late but short answer. Try this

user_count = serializers.IntegerField(
    source='user_set.count', 
    read_only=True
)
👤Lal

4👍

Everyone’s answer looks great. And I would like to contribute another options here – to use @property if-and-only-if you can modify the target model.

Assume you can modify the Group model.

class Group(models.Model):

    @property
    def user_count(self):
        return self.user_set.count

Then you can simply add 'user_count' to fields in your serializer.

I’m using this approach but I’m thinking to switch to the serializer approach as other’s answer here. Thanks everyone.

👤John Pang

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