Exception: Received incompatible instance "User Model 1"

Question

I am using Graphene-Django and trying to query a mutation.

The client side is like this:

sendMessage = async () => {
    const mutation = `mutation sendMessage($text: String!) {
                        createMessage(text: $text roomSlug: "${this.state.slug}") {
                          ok
                          message {
                            slug
                            createdDate
                            text
                            creator {
                              firstName
                              lastName
                              username
                              profilePictures {
                                file
                                pictureNumber
                              }
                            }
                          }
                        }
                      }
                    `;
    const { message, ok } = await apolloClient.mutate(mutation, {text: this.state.text})
        .then(result => result.data.createMessage);

The server side is like this:

class CreateMessage(graphene.Mutation):
    class Arguments:
        text = graphene.String(required=True)
        room_slug = graphene.String(required=True)

    ok = graphene.Boolean()
    message = graphene.Field(MessageType)

    def mutate(root, info, text, room_slug):
        if info.context.user.is_authenticated is False:
            raise PermissionDenied('Login required')

        ok = False
        room = get_object_or_404(models.Room, slug=room_slug)
        message = models.Message(room=room, creator=info.context.user, text=text)
        message.save()
        ok = True
        return CreateMessage(ok=ok, message=message)

I have no idea what things got wrong here. The mutation works when I open a built-in graphql admin view and send it through it. However, it does not work when I send the mutation through the real app and throw this error:

Exception: Received incompatible instance “User Model 1”

So I assumed it should be a client error, but apparently, the error comes from Graphene-Python, which is the server side.

I defintely have both

class MessageType(DjangoObjectType):
    class Meta:
        model = models.Message

and

class UserType(DjangoObjectType):
    class Meta:
        model = models.User

UserType is for a creator and MessageType is for a message.

Plus: the UserType works fine in every other queries and mutations. The only place it does not work is this specific mutation.

Answer 1

If anyone runs into this problem, change

message = graphene.Field(MessageType)

to

message = graphene.List(MessageType)

it should work.