title: String Related Field in DjangoRest
body: <p>I have implemented Foreign key to fetch a list of genres for movies using StringRelatedField in DRF. This however does not work while POST.
  I get <strong>StringRelatedField.to_internal_value() must be implemented</strong> as error.
  Can anyone help me?</p>
  
  <p>models.py</p>
  
  <pre><code>class Movies(models.Model):
      movie_id = models.AutoField(primary_key=True)
      movie_name = models.CharField(max_length =200)
      director = models.CharField(max_length = 100)
      popularity = models.FloatField(max_length = 3)
      imdb_score = models.FloatField(max_length = 10)
      def __unicode__(self):               
          return '%s%s%d%d' % (self.movie_name,self.director,self.popularity,self.imdb_score)
  
  class Genre(models.Model):
      genre_id = models.AutoField(primary_key=True)
      movie_name =models.ForeignKey(Movies, blank=True, null=True, on_delete=models.SET_NULL,related_name='genres')
      genre = models.CharField(max_length =40)
  
      def __unicode__(self):
          return '%s%s' % (self.genre,self.movie_name)
  </code></pre>
  
  <p>views.py</p>
  
  <pre><code>    class MovieList(viewsets.ViewSet):
                  def list(self,request):
                  try:
                      movie_list = Movies.objects.all()
                      serializer = MovieSerializer(movie_list, many=True)
                      username = request.session['username']
                      user_role = request.session['role']
                      context = {'username': username, 'user_role': user_role,     'movie_list': serializer.data}
                      return render(request, 'imdb/movie-list.html', context)
                  except KeyError:
                      pass
                      return  HttpResponseRedirect(reverse('imdb:login'))
  
  
      class AddMovie(APIView):
  
          def post(self, request, format='json'):
              data = request.data
  
              serializer = MovieSerializer(data =request.data)
              #print serializer
              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)
  </code></pre>
  
  <p>urls.py</p>
  
  <pre><code>urlpatterns = patterns('',
          url(r'^$', views.login, name='login'),
           url(r'^home/$', views.home, name='home'), 
           url(r'^logout/$', views.logout, name='logout'),
           url(r'^movie-list/$', views.MovieList.as_view({'get':'list'}),name ='movie-list'),
           url(r'^add-movie/$', views.AddMovie.as_view(),name ='add-movie') )
  </code></pre>
  
  <p>serializer.py</p>
  
  <pre><code>    class MovieSerializer(serializers.ModelSerializer):
          genres = serializers.StringRelatedField(many=True)
          class Meta:
              model = Movies
              fields = ('movie_name','director','popularity','imdb_score','genres')
  </code></pre>