Creating nested object

[areebbeigh]

Is there a way I can create a nested object without passing the ID of the parent?

e.g

POST /domains/1/nameservers
{
  domain: 1, # -> I don't want to pass this in the request
  <nameserver data>
}

[alanjds]

Yes, but you will need custom code to do it.

On some project, I am using code alike this one:

class NameserverViewset(viewsets.ModelViewSet):
    (...)
    def initialize_request(self, request, *args, **kwargs):
        request = super().initialize_request(request, *args, **kwargs)
        for querydict in [request.data, request.query_params]:
            initial_mutability = getattr(querydict, '_mutable', None)
            if initial_mutability is not None:
                querydict._mutable = True

            querydict['domain'] = kwargs['domain_pk']

            if initial_mutability is not None:
                querydict._mutable = initial_mutability
        return request

However is unclear for me if such code should be provided by drf-nested-routers as a custom viewset superclass or/and if it should be included on the docs.

What is your opinion?

[areebbeigh]

class NameserverViewset(viewsets.ModelViewSet):
    (...)
    def perform_create(self, serializer):
        serializer.save(user=self.request.user, domain_id=self.kwargs['domain_pk'])

is what I was looking for 😛 thanks.

[areebbeigh]

However is unclear for me if such code should be provided by drf-nested-routers as a custom viewset superclass or/and if it should be included on the docs.

I'd say mentioning how to get the parent pk is good enough. This looks hacky and breakable.

[nrj]

Could someone kindly post a complete solution to this with their Serializer and ViewSet please? I am not seeing this work at all. For me the perform_create is never called. The serializer raises before it even gets to the viewset with: {"domain":["This field is required."]}

Here is my Serializer and ViewSet:

class NamespaceSerializer(serializers.ModelSerializer):
    class Meta:
        model = Namespace
        fields = '__all__'

class NamespaceViewSet(viewsets.ModelViewSet):
    serializer_class = NamespaceSerializer

    def perform_create(self, serializer):
        serializer.save(domain_id=self.kwargs['domain_pk'])

So it seems that first the serializer validation must pass before perform_create is called. But if your foreign key is a required field (a very common use case) then the validation won't pass unless your post data contains the parents id.

[areebbeigh]

Could someone kindly post a complete solution to this with their Serializer and ViewSet please? I am not seeing this work at all. For me the perform_create is never called. The serializer raises before it even gets to the viewset with: {"domain":["This field is required."]}

Here is my Serializer and ViewSet:

class NamespaceSerializer(serializers.ModelSerializer):
    class Meta:
        model = Namespace
        fields = '__all__'

class NamespaceViewSet(viewsets.ModelViewSet):
    serializer_class = NamespaceSerializer

    def perform_create(self, serializer):
        serializer.save(domain=self.kwargs['domain_pk'])

So it seems that first the serializer validation must pass before perform_create is called. But if your foreign key is a required field (a very common use case) then the validation won't pass unless your post data contains the parents id.

I guess you need to set required=False for the domain field in your serializer. The error would be in creating a serializer object if you go through the stack trace.

[nrj]

Ok I see. Another solution which I've opted for is to just remove the field from the list, since the value is not POSTed I guess this makes sense anyways. Here is the solution for anyone else:

class NamespaceSerializer(serializers.ModelSerializer):
    class Meta:
        model = Namespace
        fields = [field.name for field in model._meta.fields]
        fields.remove('domain')    # don't validate this field

I was originally under the impression that I would get validation of the domain_pk in the url via the serializer:

class NamespaceSerializer(serializers.ModelSerializer):
    # synthesized field validator 
    domain = serializers.PrimaryKeyRelatedField(queryset=Domain.objects.all())

This appears not to be the case. Might be worth mentioning some of this in the docs.

[nrj]

Since this is somewhat related, is there a recommended way to perform validation of the parent primary key in the URL?

With the above solution, making a POST to say /domains/999/nameservers/ will raise if there is no domain with id=999

Where would it be best to handle this Exception?