to_representation() must be implemented (Tutorial part 5)

[Matt Sencenbaugh]

Hey guys,

I've been following the tutorial for REST Framework 3.0 (although substituting 'snippets' with my own model 'articles' which is a representation of a news article), but I'm getting hung up on an error in part 5 when changing the serializer to a HyperlinkedModelSerializer. The exact error when I try to hit any article endpoint is:

NotImplementedError at /articles/

to_representation() must be implemented.

Relevant code..

Models.py

from django.db import models

class Article(models.Model):

    owner = models.ForeignKey('auth.User', related_name='articles')

    created = models.DateTimeField(auto_now_add=True)

    published = models.DateTimeField(auto_now_add=True)

    title = models.CharField(max_length=250)

    author = models.CharField(max_length=100)

    #content contains raw html that will be rendered at a special endpoint

    content = models.TextField()

    class Meta:

        ordering = ('created',)

Serializers.py

from rest_framework import serializers

from shittr_api.models import Article

from django.contrib.auth.models import User

class ArticleSerializer(serializers.HyperlinkedModelSerializer):

    owner = serializers.Field(source='owner.username')

    render = serializers.HyperlinkedIdentityField(view_name='article-render', format='html')

    class Meta:

        model = Article

        fields = ('url', 'render', 'title', 'author', 'content', 'owner')

class UserSerializer(serializers.HyperlinkedModelSerializer):

    articles = serializers.HyperlinkedRelatedField(many=True, view_name='article-detail', read_only=True)

    class Meta:

        model = User

        fields = ('url', 'username', 'articles')

Views.py

from shittr_api.models import Article

from shittr_api.serializers import ArticleSerializer

from shittr_api.serializers import UserSerializer

from shittr_api.permissions import IsOwnerOrReadOnly

from rest_framework.decorators import api_view

from rest_framework.response import Response

from rest_framework.reverse import reverse

from rest_framework import generics

from rest_framework import permissions

from django.contrib.auth.models import User

from rest_framework import renderers

from rest_framework.response import Response

@api_view(('GET',))

def api_root(request, format=None):

    return Response({

        'users': reverse('user-list', request=request, format=format),

        'articles': reverse('article-list', request=request, format=format)

    })

class UserList(generics.ListCreateAPIView):

    queryset = User.objects.all()

    serializer_class = UserSerializer

class UserDetail(generics.RetrieveAPIView):

    queryset = User.objects.all()

    serializer_class = UserSerializer

class ArticleList(generics.ListCreateAPIView):

    queryset = Article.objects.all()

    serializer_class = ArticleSerializer

    permission_classes = (permissions.IsAuthenticatedOrReadOnly,)

    def perform_create(self, serializer):

        serializer.save(owner=self.request.user)

class ArticleDetail(generics.RetrieveUpdateDestroyAPIView):

    queryset = Article.objects.all()

    serializer_class = ArticleSerializer

    permission_classes = (permissions.IsAuthenticatedOrReadOnly, IsOwnerOrReadOnly)

class ArticleRender(generics.GenericAPIView):

    queryset = Article.objects.all()

    renderer_classes = (renderers.StaticHTMLRenderer,)

    def get(self, request, *args, **kwargs):

        article = self.get_object()

        return Response(article.content)

Urls.py

from django.conf.urls import patterns, url

from rest_framework.urlpatterns import format_suffix_patterns

from shittr_api import views

from django.conf.urls import include

urlpatterns = [

url(r'^$', views.api_root),

    url(r'^articles/$', views.ArticleList.as_view(),name='article-list'),

    url(r'^articles/(?P<pk>[0-9]+)$', views.ArticleDetail.as_view(),name='article-detail'),

url(r'^articles/(?P<pk>[0-9]+)/render/$', views.ArticleRender.as_view(),name='article-render'),

    url(r'^users/$', views.UserList.as_view(),name='user-list'),

url(r'^users/(?P<pk>[0-9]+)/$', views.UserDetail.as_view(),name='user-detail'),

]

urlpatterns += [

    url(r'^api-auth/', include('rest_framework.urls', namespace='rest_framework')),

]

Permissions.py

from rest_framework import permissions

class IsOwnerOrReadOnly(permissions.BasePermission):

    """

    Custom permission to allow only owners to edit objects

    """

    def has_object_permission(self, request, view, obj):

        if request.method in permissions.SAFE_METHODS:

            return True

        return obj.owner == request.user

Any idea what's going on?

[Tom Christie]

Hi Matt,

`serializers.Field` there should have been changed to `serializers.ReadOnlyField` for 3.0.

I've gone and made that fix now.

Thanks for raising the issue!

  Tom

[Matt Sencenbaugh]

Thanks for the quick reply, all working now!

[Scot Hacker]

On Thursday, December 11, 2014 1:43:20 AM UTC-8, Tom Christie wrote:

Hi Matt,

`serializers.Field` there should have been changed to `serializers.ReadOnlyField` for 3.0.

I've gone and made that fix now.

Thanks for raising the issue!

Ah yes, that does fix it, thanks. This is a pretty confusing error when upgrading from 2.4.x to 3.0.x as the traceback doesn't give any clue as to where in one's codebase (which class, which field) is triggering the error.

./s