django-rest-framework-json-api dynamic filter relationship

README.md

I needed to be able to filter which items of a ManyRelatedField were returned, based on some attributes of the request user. Normally, all items in the relationship are returned, however I was able to override the ManyRelatedField.to_attribute() function to enable additional filtering of the relationship.

serializers.py

from rest_framework.relations import MANY_RELATION_KWARGS, ManyRelatedField
from rest_framework import serializers
from rest_framework_json_api.relations import ResourceRelatedField


class CustomManyRelatedField(ManyRelatedField):

    def get_attribute(self, instance):
        # Override the default implementation of get_attribute
        # Can't have any relationships if not created
        if hasattr(instance, 'pk') and instance.pk is None:
            return []

        relationship = get_attribute(instance, self.source_attrs)
        queryset = self.filter_relationship(instance, relationship)
        return queryset.all() if (hasattr(queryset, 'all')) else queryset

    def filter_relationship(self, instance, relationship):
        user = self.context['request'].user
        return relationship.filter("some additional logic here")


class CustomResourceRelatedField(ResourceRelatedField):

    @classmethod
    def many_init(cls, *args, **kwargs):
        list_kwargs = {'child_relation': cls(*args, **kwargs) }
        for key in kwargs.keys():
            if key in MANY_RELATION_KWARGS:
                list_kwargs[key] = kwargs[key]
        return CustomManyRelatedField(**list_kwargs)


class BuildSerializer(serializers.ModelSerializer):
    artifacts = CustomResourceRelatedField(queryset=BuildArtifact.objects, many=True)

    class Meta:
        model = Build

Thanks a million, this worked great! I modified slightly to filter out objects that have an "is_deleted" flag set to true (and changed super call to work with Python 2.x):

class IgnoreDeletedManyRelatedField(ManyRelatedField):

    def get_attribute(self, instance):
        # Override the default implementation of get_attribute
        # Can't have any relationships if not created
        if hasattr(instance, 'pk') and instance.pk is None:
            return []

        relationship = super(ManyRelatedField, self).get_attribute(
            instance)
        queryset = relationship.filter(is_deleted=False)
        return queryset.all() if (hasattr(queryset, 'all')) else queryset


class IgnoreDeletedResourceRelatedField(ResourceRelatedField):

    @classmethod
    def many_init(cls, *args, **kwargs):
        list_kwargs = {'child_relation': cls(*args, **kwargs) }
        for key in kwargs.keys():
            if key in MANY_RELATION_KWARGS:
                list_kwargs[key] = kwargs[key]
        return IgnoreDeletedManyRelatedField(**list_kwargs)