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Django Rest Framework – Could not resolve URL for hyperlinked relationship using view name “user-detail”

Posted by: admin November 30, 2017 Leave a comment

Questions:

I am building a project in Django Rest Framework where users can login to view their wine cellar.
My ModelViewSets were working just fine and all of a sudden I get this frustrating error:

Could not resolve URL for hyperlinked relationship using view name “user-detail”. You may have failed to include the related model in your API, or incorrectly configured the lookup_field attribute on this field.

The traceback shows:

    [12/Dec/2013 18:35:29] "GET /bottles/ HTTP/1.1" 500 76677
Internal Server Error: /bottles/
Traceback (most recent call last):
  File "/Users/bpipat/.virtualenvs/usertest2/lib/python2.7/site-packages/django/core/handlers/base.py", line 114, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/Users/bpipat/.virtualenvs/usertest2/lib/python2.7/site-packages/rest_framework/viewsets.py", line 78, in view
    return self.dispatch(request, *args, **kwargs)
  File "/Users/bpipat/.virtualenvs/usertest2/lib/python2.7/site-packages/django/views/decorators/csrf.py", line 57, in wrapped_view
    return view_func(*args, **kwargs)
  File "/Users/bpipat/.virtualenvs/usertest2/lib/python2.7/site-packages/rest_framework/views.py", line 399, in dispatch
    response = self.handle_exception(exc)
  File "/Users/bpipat/.virtualenvs/usertest2/lib/python2.7/site-packages/rest_framework/views.py", line 396, in dispatch
    response = handler(request, *args, **kwargs)
  File "/Users/bpipat/.virtualenvs/usertest2/lib/python2.7/site-packages/rest_framework/mixins.py", line 96, in list
    return Response(serializer.data)
  File "/Users/bpipat/.virtualenvs/usertest2/lib/python2.7/site-packages/rest_framework/serializers.py", line 535, in data
    self._data = [self.to_native(item) for item in obj]
  File "/Users/bpipat/.virtualenvs/usertest2/lib/python2.7/site-packages/rest_framework/serializers.py", line 325, in to_native
    value = field.field_to_native(obj, field_name)
  File "/Users/bpipat/.virtualenvs/usertest2/lib/python2.7/site-packages/rest_framework/relations.py", line 153, in field_to_native
    return self.to_native(value)
  File "/Users/bpipat/.virtualenvs/usertest2/lib/python2.7/site-packages/rest_framework/relations.py", line 452, in to_native
    raise Exception(msg % view_name)
Exception: Could not resolve URL for hyperlinked relationship using view 
name "user-detail". You may have failed to include the related model in 
your API, or incorrectly configured the `lookup_field` attribute on this 
field.

I have a custom email user model and the bottle model in models.py is:

class Bottle(models.Model):    
      wine = models.ForeignKey(Wine, null=False)
      user = models.ForeignKey(User, null=False, related_name='bottles')

My serializers:

class BottleSerializer(serializers.HyperlinkedModelSerializer):

    class Meta:
        model = Bottle
        fields = ('url', 'wine', 'user')

class UserSerializer(serializers.ModelSerializer):

    class Meta:
        model = User
        fields = ('email', 'first_name', 'last_name', 'password', 'is_superuser')

My views:

class BottleViewSet(viewsets.ModelViewSet):
    """
    API endpoint that allows bottles to be viewed or edited.
    """
    queryset = Bottle.objects.all()
    serializer_class = BottleSerializer

class UserViewSet(ListCreateAPIView):
    """
    API endpoint that allows users to be viewed or edited.
    """
    queryset = User.objects.all()
    serializer_class = UserSerializer

and finally the url:

router = routers.DefaultRouter()
router.register(r'bottles', views.BottleViewSet, base_name='bottles')

urlpatterns = patterns('',
    url(r'^', include(router.urls)),
    # ...

I don’t have a user detail view and I don’t see where this issue could come from. Any ideas?

Thanks

Answers:

Because it’s a HyperlinkedModelSerializer your serializer is trying to resolve the URL for the related User on your Bottle.
As you don’t have the user detail view it can’t do this. Hence the exception.

  1. Would not just registering the UserViewSet with the router solve your issue?
  2. You could define the user field on your BottleSerializer to explicitly use the UserSerializer rather than trying to resolve the URL. See the serializer docs on dealing with nested objects for that.
Questions:
Answers:

I came across this error too and solved it as follows:

The reason is I forgot giving “**-detail” (view_name, e.g.: user-detail) a namespace. So, Django Rest Framework could not find that view.

There is one app in my project, suppose that my project name is myproject, and the app name is myapp.

There is two urls.py file, one is myproject/urls.py and the other is myapp/urls.py. I give the app a namespace in myproject/urls.py, just like:

url(r'', include(myapp.urls, namespace="myapp")),

I registered the rest framework routers in myapp/urls.py, and then got this error.

My solution was to provide url with namespace explicitly:

class UserSerializer(serializers.HyperlinkedModelSerializer):
    url = serializers.HyperlinkedIdentityField(view_name="myapp:user-detail")

    class Meta:
        model = User
        fields = ('url', 'username')

And it solved my problem.

Questions:
Answers:

This code should work, too.

class BottleSerializer(serializers.HyperlinkedModelSerializer):

  user = UserSerializer()

  class Meta:
    model = Bottle
    fields = ('url', 'wine', 'user')

Questions:
Answers:

Maybe someone can have a look at this : http://www.django-rest-framework.org/api-guide/routers/

If using namespacing with hyperlinked serializers you’ll also need to ensure that any view_name parameters on the serializers correctly reflect the namespace. For example:

urlpatterns = [
    url(r'^forgot-password/$', ForgotPasswordFormView.as_view()),
    url(r'^api/', include(router.urls, namespace='api')),
]

you’d need to include a parameter such as view_name='api:user-detail' for serializer fields hyperlinked to the user detail view.

class UserSerializer(serializers.HyperlinkedModelSerializer):
    url = serializers.HyperlinkedIdentityField(view_name="api:user-detail")

class Meta:
    model = User
    fields = ('url', 'username')

Questions:
Answers:

Another nasty mistake that causes this error is having the base_name unnecessarily defined in your urls.py. For example:

router.register(r'{pathname}, views.{ViewName}ViewSet, base_name='pathname')

This will cause the error noted above. Get that base_name outta there and get back to a working API. The code below would fix the error. Hooray!

router.register(r'{pathname}, views.{ViewName}ViewSet)

However, you probably didn’t just arbitrarily add the base_name, you might have done it because you defined a custom def get_queryset() for the View and so Django mandates that you add the base_name. In this case you’ll need to explicitly define the ‘url’ as a HyperlinkedIdentityField for the serializer in question. Notice we are defining this HyperlinkedIdentityField ON THE SERIALIZER of the view that is throwing the error. If my error were “Could not resolve URL for hyperlinked relationship using view name “study-detail”. You may have failed to include the related model in your API, or incorrectly configured the lookup_field attribute on this field.” I could fix this with the following code.

My ModelViewSet (the custom get_queryset is why I had to add the base_name to the router.register() in the first place):

class StudyViewSet(viewsets.ModelViewSet):
    serializer_class = StudySerializer

    '''custom get_queryset'''
    def get_queryset(self):
        queryset = Study.objects.all()
        return queryset

My router registration for this ModelViewSet in urls.py:

router.register(r'studies', views.StudyViewSet, base_name='studies')

AND HERE’S WHERE THE MONEY IS! Then I could solve it like so:

class StudySerializer(serializers.HyperlinkedModelSerializer):
    url = serializers.HyperlinkedIdentityField(view_name="studies-detail")
    class Meta:
        model = Study
        fields = ('url', 'name', 'active', 'created',
              'time_zone', 'user', 'surveys')

Yep. You have to explicitly define this HyperlinkedIdentityField on itself for it to work. And you need to make sure that the view_name defined on the HyperlinkedIdentityField is the same as you defined on the base_name in urls.py with a ‘-detail’ added after it.

Questions:
Answers:

I ran into the same error while I was following the DRF quickstart guide
http://www.django-rest-framework.org/tutorial/quickstart/ and then attempting to browse to /users. I’ve done this setup many times before without problems.

My solution was not in the code but in replacing the database.

The difference between this install and the others before was when I created the local database.

This time I ran my

./manage.py migrate
./manage.py createsuperuser

immediately after running

virtualenv venv
. venv/bin/activate
pip install django
pip install djangorestframework

Instead of the exact order listed in the guide.

I suspected something wasn’t properly created in the DB. I didn’t care about my dev db so I deleted it and ran the ./manage.py migrate command once more, created a super user, browsed to /users and the error was gone.

Something was problematic with the order of operations in which I configured DRF and the db.

If you are using sqlite and are able to test changing to a fresh DB then it’s worth an attempt before you go dissecting all of your code.

Questions:
Answers:

Bottle = serializers.PrimaryKeyRelatedField(read_only=True)

read_only allows you to represent the field without having to link it to another view of the model.

Questions:
Answers:

Same Error, but different reason:

I define a custom user model, nothing new field:

from django.contrib.auth.models import (AbstractUser)
class CustomUser(AbstractUser):
    """
    custom user, reference below example
    https://github.com/jonathanchu/django-custom-user-example/blob/master/customuser/accounts/models.py

    # original User class has all I need
    # Just add __str__, not rewrite other field
    - id
    - username
    - password
    - email
    - is_active
    - date_joined
    - method, email_user
    """

    def __str__(self):
        return self.username

This is my view function:

from rest_framework import permissions
from rest_framework import viewsets
from .models import (CustomUser)
class UserViewSet(viewsets.ModelViewSet):
    permission_classes = (permissions.AllowAny,)
    serializer_class = UserSerializer

    def get_queryset(self):
        queryset = CustomUser.objects.filter(id=self.request.user.id)
        if self.request.user.is_superuser:
            queryset = CustomUser.objects.all()
        return queryset

Since I didn’t give queryset directly in UserViewSet, I have to set base_name when I register this viewset. This is where my error message caused by urls.py file:

from myapp.views import (UserViewSet)
from rest_framework.routers import DefaultRouter
router = DefaultRouter()
router.register(r'users', UserViewSet, base_name='customuser')  # <--base_name needs to be 'customuser' instead of 'user'

You need a base_name same as your model name – customuser.