How do I create multiple model instances with Djan

Question

I would like to save and update multiple instances using the Django Rest Framework with one API call. For example, let's say I have a "Classroom" model that can have multiple "Teachers". If I wanted to create multiple teachers and later update all of their classroom numbers how would I do that? Do I have to make an API call for each teacher?

I know currently we can't save nested models, but I would like to know if we can save it at the teacher level. Thanks!

Answer 1

I know this was asked a while ago now but I found it whilst trying to figure this out myself.

It turns out if you pass many=True when instantiating the serializer class for a model, it can then accept multiple objects.

This is mentioned here in the django rest framework docs

For my case, my view looked like this:

class ThingViewSet(viewsets.ModelViewSet):
    """This view provides list, detail, create, retrieve, update
    and destroy actions for Things."""
    model = Thing
    serializer_class = ThingSerializer

I didn't really want to go writing a load of boilerplate just to have direct control over the instantiation of the serializer and pass many=True, so in my serializer class I override the __init__ instead:

class ThingSerializer(serializers.ModelSerializer):
    def __init__(self, *args, **kwargs):
        many = kwargs.pop('many', True)
        super(ThingSerializer, self).__init__(many=many, *args, **kwargs)

    class Meta:
        model = Thing
        fields = ('loads', 'of', 'fields', )

Posting data to the list URL for this view in the format:

[
    {'loads':'foo','of':'bar','fields':'buzz'},
    {'loads':'fizz','of':'bazz','fields':'errrrm'}
]

Created two resources with those details. Which was nice.

Answer 2

I think the best aprouch to respect the propoused architecture of the framework will be to create a mixin like this:

class CreateListModelMixin(object):

    def create(self, request, *args, **kwargs):
        """
            Create a list of model instances if a list is provides or a
            single model instance otherwise.
        """
        data = request.data
        if isinstance(data, list):
            serializer = self.get_serializer(data=request.data, many=True)
        else:
            serializer = self.get_serializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        self.perform_create(serializer)
        headers = self.get_success_headers(serializer.data)
        return Response(serializer.data, status=status.HTTP_201_CREATED,
                    headers=headers)

Then you can override the CreateModelMixin of ModelViewSet like this:

class <MyModel>ViewSet(CreateListModelMixin, viewsets.ModelViewSet):
    ...
    ...

Now in the client you can work like this:

var things = [    
    {'loads':'foo','of':'bar','fields':'buzz'},
    {'loads':'fizz','of':'bazz','fields':'errrrm'}
]
thingClientResource.post(things)

or

var thing = {
    'loads':'foo','of':'bar','fields':'buzz'
}

thingClientResource.post(thing)

EDIT:

As Roger Collins suggest in her response is more clever to overwrite the get_serializer method than the 'create'.

Answer 3

You can simply overwrite the get_serializer method in your APIView and pass many=True into get_serializer of the base view like so:

class SomeAPIView(CreateAPIView):
    queryset = SomeModel.objects.all()
    serializer_class = SomeSerializer

    def get_serializer(self, instance=None, data=None, many=False, partial=False):
        return super(SomeAPIView, self).get_serializer(instance=instance, data=data, many=True, partial=partial)

Answer 4

Most straightforward method I've come across:

    def post(self, request, *args, **kwargs):
        serializer = ThatSerializer(data=request.data, many=isinstance(request.data, list))
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data, status=status.HTTP_201_CREATED)
        else:
            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

Answer 5

The Generic Views page in Django REST Framework's documentation states that the ListCreateAPIView generic view is "used for read-write endpoints to represent a collection of model instances".

That's where I would start looking (and I'm going to actually, since we'll need this functionality in our project soon as well).

Note also that the examples on the Generic Views page happen to use ListCreateAPIView.

Answer 6

I couldn't quite figure out getting the request.DATA to convert from a dictionary to an array - which was a limit on my ability to Tom Manterfield's solution to work. Here is my solution:

class ThingSerializer(serializers.ModelSerializer):
    def __init__(self, *args, **kwargs):
        many = kwargs.pop('many', True)
        super(ThingSerializer, self).__init__(many=many, *args, **kwargs)

    class Meta:
        model = Thing
        fields = ('loads', 'of', 'fields', )

class ThingViewSet(mixins.CreateModelMixin, viewsets.GenericViewSet ):
    queryset = myModels\
        .Thing\
        .objects\
        .all()
    serializer_class = ThingSerializer

    def create(self, request, *args, **kwargs):
        self.user = request.user
        listOfThings = request.DATA['things']

        serializer = self.get_serializer(data=listOfThings, files=request.FILES, many=True)
        if serializer.is_valid():
            serializer.save()
            headers = self.get_success_headers(serializer.data)
            return Response(serializer.data, status=status.HTTP_201_CREATED,
                            headers=headers)

        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

And then I run the equivalent of this on the client:

var things = {    
    "things":[
        {'loads':'foo','of':'bar','fields':'buzz'},
        {'loads':'fizz','of':'bazz','fields':'errrrm'}]
}
thingClientResource.post(things)