How do I create multiple model instances with Django Rest Framework?

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 came to a similar conclusion as Daniel Albarral, but here's a more succinct solution:

class CreateListModelMixin(object):

    def get_serializer(self, *args, **kwargs):
        """ if an array is passed, set serializer to many """
        if isinstance(kwargs.get('data', {}), list):
            kwargs['many'] = True
        return super(CreateListModelMixin, self).get_serializer(*args, **kwargs)

Answer 3

Here's another solution, you don't need to override your serializers __init__ method. Just override your view's (ModelViewSet) 'create' method. Notice many=isinstance(request.data,list). Here many=True when you send an array of objects to create, and False when you send just the one. This way, you can save both an item and a list!

from rest_framework import status, viewsets
from rest_framework.response import Response

class ThingViewSet(viewsets.ModelViewSet):

"""This view snippet provides both list and item create functionality."""

    #I took the liberty to change the model to queryset
    queryset = Thing.objects.all()
    serializer_class = ThingSerializer

    def create(self, request, *args, **kwargs):
        serializer = self.get_serializer(data=request.data, many=isinstance(request.data,list))
        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)

Answer 4

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)

Answer 5

I think the best approach to respect the proposed 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 provided 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 suggests in his response is more clever to overwrite the get_serializer method than the 'create'.

Answer 6

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 7

I came up with simple example in post

Serializers.py

from rest_framework import serializers
from movie.models import Movie

class MovieSerializer(serializers.ModelSerializer):

    class Meta:
        model = Movie
        fields = [
            'popularity',
            'director',
            'genre',
            'imdb_score',
            'name',
        ]  

Views.py

from rest_framework.response import Response
from rest_framework import generics
from .serializers import MovieSerializer
from movie.models import Movie
from rest_framework import status
from rest_framework.permissions import IsAuthenticated

class MovieList(generics.ListCreateAPIView):
    queryset = Movie.objects.all().order_by('-id')[:10]
    serializer_class = MovieSerializer
    permission_classes = (IsAuthenticated,)

    def list(self, request):
        queryset = self.get_queryset()
        serializer = MovieSerializer(queryset, many=True)
        return Response(serializer.data)

    def post(self, request, format=None):
        data = request.data
        if isinstance(data, list):  # <- is the main logic
            serializer = self.get_serializer(data=request.data, many=True)
        else:
            serializer = self.get_serializer(data=request.data)
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data, status=status.HTTP_201_CREATED)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

These line are the actual logic of Multiple Instance -

data = request.data
if isinstance(data, list):  # <- is the main logic
      serializer = self.get_serializer(data=request.data, many=True)
else:
      serializer = self.get_serializer(data=request.data)

If you are confused with many=True, see this

When we send data it will be inside list somewhat like this -

[
    {
        "popularity": 84.0,
        "director": "Stanley Kubrick",
        "genre": [
            1,
            6,
            10
        ],
        "imdb_score": 8.4,
        "name": "2001 : A Space Odyssey"
    },
    {
        "popularity": 84.0,
        "director": "Stanley Kubrick",
        "genre": [
            1,
            6,
            10
        ],
        "imdb_score": 8.4,
        "name": "2001 : A Space Odyssey"
    }
]

Answer 8

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 9

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)