How do I use perform_create to set a field automatically in Django Rest Framework?

Question

I am trying to create a REST Api for my application.

urls.py in the application directory looks like this:

urlpatterns = [
    url(
        r'^professors/(?P<pk>[0-9]+)/reviews/$',
        views.ProfessorReviewList.as_view(),
        name = 'user-review-list',
    )
]

serializers.py

class ProfessorSerializer(serializers.HyperlinkedModelSerializer):
    reviews = serializers.HyperlinkedIdentityField(view_name='professor-review-list')
    class Meta:
        model = Professor
        fields = (
            'url', 'name', 'name_code', 'university',
            'department', 'total_rating_points',
            'number_of_reviews', 'rating', 'reviews',
        )

class ReviewSerializer(serializers.HyperlinkedModelSerializer):
    author = serializers.ReadOnlyField(source='author.username')

    class Meta:
        model = Review
        fields = (
            'url', 'author', 'professor',
            'created', 'updated', 'rating', 'text'
        )

And finally, my views.py looks like this:

class ProfessorReviewList(generics.ListCreateAPIView):
    queryset = Review.objects.all()
    serializer_class = ReviewSerializer
    def get_queryset(self):
        queryset = super(ProfessorReviewList, self).get_queryset()
        return queryset.filter(professor__pk=self.kwargs.get('pk'))

    permission_classes = (permissions.IsAuthenticatedOrReadOnly,
                          IsAuthorOrReadOnly,)

    def perform_create(self, serializer):
        # The request user is set as author automatically.
        serializer.save(author=self.request.user)

What I am trying to do is get a list of all the reviews for one particular professor when I go to the URL. I also want to allow users to add a new review at this end-point if they want to. Everything works nicely, but I want a system where the user does not have to choose the professor when creating a review.

Lets say I go to /professors/1/reviews/, a list of all the reviews for the professor with pk=1 is obtained. Now, if the user adds a new review, the professor is automatically set to the professor with pk=1. The user does not get to choose. At /professors/2/reviews/, the professor field for the review is automatically set to the professor with pk=2 and so on and so on.

How can I do this? Thanks for any help.

Answer 1

You should simply add the professor as you did with the author:

serializer.save(
    author=self.request.user,
    professor_id=self.kwargs.get('pk'),
)

Note that in order to avoid to pull the professor from the DB, I set the FK explicitly instead.