I don't understand that keyerror occurs in my code in django

Question

I am using the django rest framework modelviewset to re-turn the entire post when I request get. But after writing the code, I sent the get request and the following error appears.

Traceback (most recent call last):
      File "C:\Users\kurak\AppData\Local\Programs\Python\Python38-32\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
        response = get_response(request)
      File "C:\Users\kurak\AppData\Local\Programs\Python\Python38-32\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
        response = self.process_exception_by_middleware(e, request)
      File "C:\Users\kurak\AppData\Local\Programs\Python\Python38-32\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
        response = wrapped_callback(request, *callback_args, **callback_kwargs)
      File "C:\Users\kurak\AppData\Local\Programs\Python\Python38-32\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
        return view_func(*args, **kwargs)
      File "C:\Users\kurak\AppData\Local\Programs\Python\Python38-32\lib\site-packages\rest_framework\viewsets.py", line 114, in view
        return self.dispatch(request, *args, **kwargs)
      File "C:\Users\kurak\AppData\Local\Programs\Python\Python38-32\lib\site-packages\rest_framework\views.py", line 505, in dispatch
        response = self.handle_exception(exc)
      File "C:\Users\kurak\AppData\Local\Programs\Python\Python38-32\lib\site-packages\rest_framework\views.py", line 465, in handle_exception
        self.raise_uncaught_exception(exc)
      File "C:\Users\kurak\AppData\Local\Programs\Python\Python38-32\lib\site-packages\rest_framework\views.py", line 476, in raise_uncaught_except

ion
    raise exc
  File "C:\Users\kurak\AppData\Local\Programs\Python\Python38-32\lib\site-packages\rest_framework\views.py", line 502, in dispatch
    response = handler(request, *args, **kwargs)
  File "D:\school\대회 및 프로젝트\CoCo\feed\views.py", line 23, in list
    'email': serializer.data['author_email'],
KeyError: 'author_email'

I have clearly stated this in the serializer, but I don't understand why a keyerror appears. Can you tell me what the problem is in my code? Here's my code. Thank in advance.

views.py

class CreateReadPostView (ModelViewSet) :
    serializer_class = PostSerializer
    permission_classes = [IsAuthenticated]
    queryset = Post.objects.all()

    def perform_create (self, serializer) :
        serializer.save(author=self.request.user)

    def list (self, request) :
        serializer = self.serializer_class(data=request.data)
        serializer.is_valid(raise_exception=True)
        
        data = {
            'author': {
                'email': serializer.data['author_email'],
                'username': serializer.data['author_username'],
                'profile': serializer.data['author_profile']
            },
            'title': serializer.data['title'],
            'text': serializer.data['text'],
            'images': serializer.data['image'],
            'view': serializer.data['view'],
            'tag': serializer.data['tag']
        }

        return Response(data, status=200)

serializers.py

class PostSerializer (serializers.ModelSerializer) :
    author_username = serializers.CharField(source='author.username', read_only=True)
    author_email = serializers.CharField(source='author.email', read_only=True)
    author_profile = serializers.ImageField(source='author.profile', read_only=True, use_url=True)
    title = serializers.CharField(allow_null=True)
    text = serializers.CharField(allow_null=True)
    image = ImageSerializer(many=True, read_only=True)

    class Meta:
        model = Post
        fields = [
            'author_username',
            'author_email',
            'author_profile',
            'title', 
            'text', 
            'image', 
            'view'
        ]

Answer 1

The problem is how you defined your list method. Please use the default list method in the viewset as a reference to define yours. Specifically, you are initializing the serializer with request.data, when there is no data in the request because it is a GET request. This is only done in the POST/PUT/PATCH requests when you want to serialize the input and create a new object with the data. Instead, you should pass in the queryset that should be serialized for output.There is KeyError because author_email is readonly and you initialized the serializer in write mode so of course, the author-email is not available.

I would advice that you instead keep the inbuilt list method and use a nested representation in the serializers like this:

class AuthorSerializer(serializers.ModelSerializer):
    class Meta:
        model = Author
        fields = ('username', 'email', 'profile')

class PostSerializer (serializers.ModelSerializer) :
    author = AuthorSerializer(read_only=True)
    title = serializers.CharField(allow_null=True)
    text = serializers.CharField(allow_null=True)
    image = ImageSerializer(many=True, read_only=True)

    class Meta:
        model = Post
        fields = [
            'author',
            'title', 
            'text', 
            'image', 
            'view'
        ]
      

Then you can have a simple viewset:

class CreateReadPostView (ModelViewSet) :
    serializer_class = PostSerializer
    permission_classes = [IsAuthenticated]
    queryset = Post.objects.all()

    def perform_create (self, serializer) :
        serializer.save(author=self.request.user)

To understand more about how the list method is implemented, check the ListMixin. It fetches the queryset, applies filters and then paginates them. These are things you ommitted in your code