title: Django - objects.values() and prefetch_related() in same query
body: <p>I have Book, Profile, Book_stat model as below. I am trying to minimize the fields from <code>Book</code> model and prefetch_related method to get the data from <code>Book_stat</code> model.  </p>
  
  <p><strong>models.py</strong>  </p>
  
  <pre><code>class Book(models.Model):
      title = models.CharField(max_length=200)
      image = models.FileField(upload_to="mp/", blank=True)
  
      def __str__(self):
          return self.title
  
  class Profile(models.Model):
      user = models.OneToOneField(User, on_delete=models.CASCADE)
      full_name = models.CharField(max_length=150)
  
      def __str__(self):
          return self.full_name
  
  class Book_stat(models.Model):
      user = models.ForeignKey(User)
      book = models.ForeignKey(Book)
      rating = models.DecimalField(max_digits=5, decimal_places=2, default=Decimal('0.00'))
      like = models.BooleanField(default=False)
  
      def __str__(self):
          return self.book.title + ' by: ' + self.user.profile.full_name  
  </code></pre>
  
  <p><strong>views.py</strong>  </p>
  
  <pre><code>def books(request):
      books = books = Book.objects.prefetch_related('book_stat_set').values('id','title', 'image')
      for book in books:
          for book_stat in book.book_stat_set.all(): # error: 'dict' object has no attribute 'book_stat_set'
              book.stats = book_stat
              pprint(vars(book_stat))
      return HttpResponse(books, content_type= 'json')
  </code></pre>
  
  <p><strong>1)</strong> I would like to send the <code>json response</code> to front end as below<br>
  <strong>2)</strong> If possible i want to use <code>book_stat_set.values('like', 'rating')</code> instead of <code>book_stat_set.all()</code> so that i query for <code>like</code>, <code>rating</code> only</p>
  
  <pre><code>books = [
      {
          id: 1,
          title: 'some title1',
          image: 'image1.jpg',
          stats: {
              like: true,
              rating: 3.50
          }
      },
      {
          id: 2,
          title: 'some title2',
          image: 'image1.jpg',
          stats: {
              like: true,
              rating: 3.50
          }
      }
  ]
  </code></pre>