feat: assign category to media post-serialization

Changed the approach to assigning a category to an uploaded media file
by fetching the Category instance from the database after the media file
has been serialized and saved. This ensures that the category assigned
is validated against existing categories in the database, enhancing data
integrity and error handling when an incorrect category is specified.
Previously, the assignment used a direct extraction from request
arguments which might not have validated the category's existence.

quackscape/users/views.py

@@ -86,9 +86,9 @@ class FileUploadView(GenericAPIView):
         serializer = serializer_class(data=request.data)
 
         if serializer.is_valid():
-            instance.category = request.kwargs["category"]
             instance = serializer.save()
-            instance.refresh_from_db()
+            instance.category = Category.objects.get(id=kwargs["category"])
+            instance.save()
             return Response(OriginalMediaSerializer(instance).data, status=status.HTTP_201_CREATED)
 
         else: