Examples on adding calculated fields

Exposing fields that are in the db/model works fine, but what about calculated fields? For example, if I want to expose a field called Author.book_count that will obviously not be queriable or editable, how can I do that?

[Jufik]

@skorokithakis checkout issue this issue: https://github.com/graphql-python/graphene/issues/101

Import graphene and do: vote_count = graphene.Int(source='vote_count')

‘vote_count’ is my property.

Full code:

class QuestionNode(DjangoObjectType):
    vote_count = graphene.Int(source='vote_count')
    class Meta:
        model = Question
        # filter_fields = ['name', 'ingredients']
        interfaces = (relay.Node, )

[mvanlonden]

@paymog

    def resolve_project(self, info, name):

        if id is not None:
            project = Project.objects.get(pk=id) # how do I populate `extra_field` here?
            return ProjectType(**project, extra_field="something")


        return None