Django Rest Framework - can't created object with existing FK reference - django-rest-framework

Question

I have a serializer class in DRF like so:
class ProjectSerializer(serializers.HyperlinkedModelSerializer):
created_by = UserSerializer() # created_by is an FK to User model
class Meta:
model = Project
fields = ('id', 'title', 'created_by')
My views:
class ProjectList(generics.ListCreateAPIView):
model = Project
serializer_class = ProjectSerializer
filter_fields = ('title',)
def post(self, request, format=None):
serializer = ProjectSerializer(data={
"id": 12,
"title": "FooBar's Project",
"created_by": {
"id": 1,
"username": "foobar",
"first_name": "foo",
"last_name": "bar",
},
})
if serializer.is_valid():
serializer.save()
else:
print serializer.errors
return Response(serializer.data, status=status.HTTP_201_CREATED)
This works almost as expected except that DRF complains that:
{'created_by': [{'username': [u'User with this Username already exists.']}]}
What I want is that the Project is created with reference to an existing user. What am I doing wrong here?
Note: I am tracking trunk for DRF, not from the cheeseshop.

Answer 1

If you want to assign an existing user, not creating one, nested serializer is not the way. As you want to just add the relation to the user, you will need to take a look at relations.
The PrimaryKeyRelatedField is way to go and since this field is going to be writable you will also need to pass a queryset attribute.
created_by = serializers.PrimaryKeyRelatedField(queryset=User.objects.all())
See the documentation to check the additional options that can be passed to this field:
http://django-rest-framework.org/api-guide/relations#primarykeyrelatedfield
Then your example post could look like this:
def post(self, request, format=None):
user = User.objects.get(pk=8)
serializer = ProjectSerializer(data={
"id": 12,
"title": "FooBar's Project",
"created_by": user.pk,
})

Answer 2

(Posted on behalf of the question author).
This is the working solution:
# serializers.py
class ProjectSerializer(serializers.HyperlinkedModelSerializer):
...
created_by = serializers.PrimaryKeyRelatedField(
queryset=User.objects.all()
)
class Meta:
model = Project
fields = ('id', 'title', 'created_by')
# views.py
class ProjectList(generics.ListCreateAPIView):
model = Project
serializer_class = ProjectSerializer
filter_fields = ('title',)
def post(self, request, format=None):
serializer = ProjectSerializer(data={
"title": request.DATA.get('title'),
"created_by": request.user.pk,
})
if serializer.is_valid():
serializer.save()
else:
return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
return Response(serializer.data, status=status.HTTP_201_CREATED)