Graphene Django is an easy to use library for writing GraphQL APIs within Django. But some of the documentation for Graphene is less than great.
When I was learning Graphene Django, I originally found it very hard to expose an
@property value of my model to the GraphQL API. This article will look into how to do that, and also why it works.
Say you have a Poll object, and you added a URL property:
class Poll(models.Model): ... @property def url(self): return 'https://pollsite/polls/' + id
Then you can simply add a line to specify its existence in the schema:
class PollType(DjangoObjectType): class Meta: model = models.Poll interfaces = (relay.Node,) # This is it, so simple and so functional: url = graphene.String()
That's it. Just use the form
property_name = graphene.DataType(). You can even use more fancy datatypes, like a
graphene.List(graphene.Int()). There is a good reference to check it out.
First, we need to understand the resolver of the property. By default, the resolvers perform a
getattr lookup on the object. This means it would like be this if we were to write it manually:
url = graphene.String() def resolve_url(self, args, context, info): return self.url
But that code looks stupid! Isn't the url attribute the
graphene.String()? Isn't that code broken?
self in a resolver doesn't represent an instance of the class. Or maybe it does. Anyway; Graphene is a festival of metaclass programming. So the
self object is really the Django object, not your graphene object! Once I found that out, it all started to make a lot more sense to me.
Well, that's a very quick dive into the weird and wonderful world of the Graphene framework. Metaclass magic hey!
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