Django GraphQL subscription not returning any data

Question

I'm using Graphene, Django and graphene-subscriptions to define a GraphQL Subscription. I'm trying to receive updates whenever a new Book with a specific Author is created. I've followed the getting started guide, and I'm trying to use the following code:

class SubscriptionBook(graphene.ObjectType):
    NewBooks = graphene.Field(BookType, Author = graphene.String(required=True))

    def resolve_NewBooks(root, info, Author):

        return root.filter( 
            lambda event:
                event.operation == CREATED  and
                isinstance(event.instance, Book) and
                event.instance.AuthorID == Author
        ).map(lambda event: event.instance)

But it doesn't seem to work. It appears that this line is failing:

event.instance.AuthorID == Author

What am I doing wrong?

Answer 1

One of the common problems I've run into when defining subscriptions like this is having a type mismatch when filtering by id.

Because Author is a string, if event.instance.AuthorID is a Django primary key (an int value), then

event.instance.AuthorID == Author

will return False.

You can fix this by type-casting the Author value to an int like so:

event.instance.AuthorID == int(Author)