Include intermediary (through model) in responses in Django Rest Framework

Question

How about.....

On your MemberSerializer, define a field on it like:

groups = MembershipSerializer(source='membership_set', many=True)

and then on your membership serializer you can create this:

class MembershipSerializer(serializers.HyperlinkedModelSerializer):

    id = serializers.Field(source='group.id')
    name = serializers.Field(source='group.name')

    class Meta:
        model = Membership

        fields = ('id', 'name', 'join_date', )

That has the overall effect of creating a serialized value, groups, that has as its source the membership you want, and then it uses a custom serializer to pull out the bits you want to display.

EDIT: as commented by @bryanph, serializers.field was renamed to serializers.ReadOnlyField in DRF 3.0, so this should read:

class MembershipSerializer(serializers.HyperlinkedModelSerializer):

    id = serializers.ReadOnlyField(source='group.id')
    name = serializers.ReadOnlyField(source='group.name')

    class Meta:
        model = Membership

        fields = ('id', 'name', 'join_date', )

for any modern implementations

I was facing this problem and my solution (using DRF 3.6) was to use SerializerMethodField on the object and explicitly query the Membership table like so:

class MembershipSerializer(serializers.ModelSerializer):
    """Used as a nested serializer by MemberSerializer"""
    class Meta:
        model = Membership
        fields = ('id','group','join_date')

class MemberSerializer(serializers.ModelSerializer):
    groups = serializers.SerializerMethodField()

    class Meta:
        model = Member
        fields = ('id','name','groups')

    def get_groups(self, obj):
        "obj is a Member instance. Returns list of dicts"""
        qset = Membership.objects.filter(member=obj)
        return [MembershipSerializer(m).data for m in qset]

This will return a list of dicts for the groups key where each dict is serialized from the MembershipSerializer. To make it writable, you can define your own create/update method inside the MemberSerializer where you iterate over the input data and explicitly create or update Membership model instances.