There's some way to set the `source` field param for nested fields?

[alexcmgit]

Context

I'm currently trying to set my model user User subfield user.actor.id as field source of my DjangoObjectType.

This happens because there's other kind of users within the application like an Organization or even a Bot (all of them are actors).

Example

Lets define a custom Type:

class User(DjangoObjectType):
    class Meta:
        model = UserModel
        exclude = ['actor']
        filter_fields = ['actor__login']
        interfaces = [graphene.relay.Node]
        skip_registry = True

    # The login field is originated from `actor` relationship, not from the user model itself.
    # It doesn't work, actor__login is interpreted as user field [user.actor__login] not [user.actor.login].
    login = graphene.Field(graphene.String, source='actor__login')
    # ...

In the example above I define the login field source as source='actor__login' but I saw that here we're using getattr function to resolve the source so it's currently impossible to set the field without defining a custom resolver.

https://github.com/graphql-python/graphene/blob/dfece7f65d4bad51a87a8e9f03f9acef1e25d3f8/graphene/types/field.py#L16-L20

I would like to know if there's an alternative solution to select a subfield like the example or we're forced to create a custom resolver by using the resolver=lambda _, __: ... arg or the class method declaration.

Thanks for the hard work and the library!

[erikwrede]

I think you'll need to create a resolver returning root.actor.login/resolving the actor first depending on your setup.

[alexcmgit]

Yeah, but since it's only field configuration I created a function to generate the resolver itself:

def subfield(source, separator='.'):
    def resolver(self, info, *args, **kwargs):
        value = self
        for part in source.split(separator):
            value = getattr(value, part)
        return value

    return resolver


def source(source, separator='.'):
    return {'resolver': subfield(source, separator)}

Usage:

class User(DjangoObjectType):
    class Meta:
        model = UserModel
        exclude = ['actor']
        filter_fields = ['actor__login']
        interfaces = [Node]
        skip_registry = True

    login = graphene.Field(graphene.String, **source('actor.login'))
    # ...

[erikwrede]

Sorry for the late reply, didn't get the notification. Looks interesting! Do you want to open a PR and integrate it into the main repo?