Adding root element to json response (django-rest-framework)

Question

I am trying to determine the best way to add a root element to all json responses using django and django-rest-framework.

I think adding a custom renderer is the best way to accomplish what I want to achieve and this is what I have come up with so far:

from rest_framework.renderers import JSONRenderer

class CustomJSONRenderer(JSONRenderer):
#override the render method
def render(self, data, accepted_media_type=None, renderer_context=None):
    #call super, as we really just want to mess with the data returned
    json_str = super(CustomJSONRenderer, self).render(data, accepted_media_type, renderer_context)
    root_element = 'contact'

    #wrap the json string in the desired root element
    ret = '{%s: %s}' % (root_element, json_str) 

    return ret

The tricky part now is dynamically setting the root_element based on the view that render() is being called from.

Any pointers/advice would be greatly appreciated,

Cheers

Answer 1

For posterity, below is the final solution. It has grown slightly from the original as it now reformats paginated results as well.

Also I should have specified before, that the reason for the JSON root element is for integration with an Ember front end solution.

serializer:

from rest_framework.serializers import ModelSerializer
from api.models import Contact

class ContactSerializer(ModelSerializer):
    class Meta:
        model = Contact
        #define the resource we wish to use for the root element of the response
        resource_name = 'contact' 
        fields = ('id', 'first_name', 'last_name', 'phone_number', 'company')

renderer:

from rest_framework.renderers import JSONRenderer

class CustomJSONRenderer(JSONRenderer):
    """
        Override the render method of the django rest framework JSONRenderer to allow the following:
        * adding a resource_name root element to all GET requests formatted with JSON
        * reformatting paginated results to the following structure {meta: {}, resource_name: [{},{}]}

        NB: This solution requires a custom pagination serializer and an attribute of 'resource_name'
        defined in the serializer
    """
    def render(self, data, accepted_media_type=None, renderer_context=None):
        response_data = {}

        #determine the resource name for this request - default to objects if not defined
        resource = getattr(renderer_context.get('view').get_serializer().Meta, 'resource_name', 'objects')

        #check if the results have been paginated
        if data.get('paginated_results'):
            #add the resource key and copy the results
            response_data['meta'] = data.get('meta')
            response_data[resource] = data.get('paginated_results')
        else:
            response_data[resource] = data

        #call super to render the response
        response = super(CustomJSONRenderer, self).render(response_data, accepted_media_type, renderer_context)

        return response

pagination:

from rest_framework import pagination, serializers

class CustomMetaSerializer(serializers.Serializer):
    next_page = pagination.NextPageField(source='*')
    prev_page = pagination.PreviousPageField(source='*')
    record_count = serializers.Field(source='paginator.count')

class CustomPaginationSerializer(pagination.BasePaginationSerializer):
    # Takes the page object as the source
    meta = CustomMetaSerializer(source='*')
    results_field = 'paginated_results'

Answer 2

Credit to ever.wakeful for getting me 95% of the way there.

Personally, I wanted to add meta data to every api request for a certain object, regardless of whether or not it was paginated. I also wanted to simply pass in a dict object that I defined manually.

Tweaked Custom Renderer

class CustomJSONRenderer(renderers.JSONRenderer):
    def render(self, data, accepted_media_type=None, renderer_context=None):
        response_data = {}
        # Name the object list 
        object_list = 'results'
        try:
            meta_dict = getattr(renderer_context.get('view').get_serializer().Meta, 'meta_dict')
        except:
            meta_dict = dict()
        try:
            data.get('paginated_results')
            response_data['meta'] = data['meta']
            response_data[object_list] = data['results']
        except:
            response_data[object_list] = data
            response_data['meta'] = dict()
            # Add custom meta data
            response_data['meta'].update(meta_dict)
            # Call super to render the response
            response = super(CustomJSONRenderer, self).render(response_data, accepted_media_type, renderer_context)
        return response

Parent Serializer and View Example

class MovieListSerializer(serializers.ModelSerializer):
    class Meta:
        model = Movie
        meta_dict = dict()
        meta_dict['foo'] = 'bar'

class MovieViewSet(generics.ListAPIView):
    queryset = Movie.objects.exclude(image__exact = "")
    serializer_class = MovieListSerializer
    permission_classes = (IsAdminOrReadOnly,)
    renderer_classes = (CustomJSONRenderer,)
    pagination_serializer_class = CustomPaginationSerializer
    paginate_by = 10