How to raise 404 as a status code in Serializer Validate function in DRF?

I have written a validate() function inside my serializer. By default, Serializer Errors return 400 as a status code. But I want to return 404. I tried this:

class MySerializer(serializers.ModelSerializer):
    class Meta:
        model = models.MyClass
        fields = "__all__"

    def validate(self, data):
        current_user = self.context.get("request").user
        user = data.get("user")
        if user!=current_user:
            raise ValidationError({'detail': 'Not found.'}, code=404)
        return data  

But it still returns 400 as a response in status code. How to do it?

You can do it from view by handling the serializes validation:

class MySerializer(serializers.ModelSerializer):

    class Meta:
        model = models.MyClass
        fields = "__all__"

    def validate(self, data):
        current_user = self.context.get("request").user
        user = data.get("user")
        if user != current_user:
            raise serializers.ValidationError(
                {'detail': 'Not found.'},
                code=404,
            )
        return data


class MyView(APIView):

    def post(self, request):
        serializer = MySerializer(
            data=request.data,
            context={'request': request},
        )
        if not serializer.is_valid():
            return Response(serializer.errors, status=404)
        return Response(serializer.data)

Alternately you can do it by defining own exception handler:

def my_exception_handler(exc, context):
    response = exception_handler(exc, context)
    if response is not None and response.status_code == 400:
        response.status_code = 404
    return response

class MyView(APIView):
    exception_handler = my_exception_handler

    def post(self, request):
        serializer = MySerializer(
            data=request.data, 
            context={'request': request},
        )
        serializer.is_valid(raise_exception=True)
        return Response(serializer.data)

But as you said, if you want to do it from serializer, then you have to define custom exception and raise it from serialize :

class NotFoundError(serializers.ValidationError):
    def __init__(self, detail):
        super().__init__(detail, code=404)


class MySerializer(serializers.ModelSerializer):
    class Meta:
        model = models.MyClass
        fields = "__all__"

    def validate(self, data):
        current_user = self.context.get("request").user
        user = data.get("user")
        if user != current_user:
            raise NotFoundError({'detail': 'Not found.'})
        return data