Add setting for including foreignkey IDs

[spockNinja]

Problem

By default, relations are only exposed as complex nested structures. So in order to get a related ID, you have to perform the join to the related field. Sometimes, only the id is needed at first, and the related object might be fetched by id later on an as-needed basis.

Solution

Add a new setting, INCLUDE_FOREIGNKEY_IDS that tells graphene-django to add graphene.ID fields for foreign keys.

Utilize this new option in construct_fields to look for ForeignKey fields and add them along with their existing relational field.

Current Behavior

{
  myObjects {
    relatedObject {
      id
    }
  }
}

Current Workaround

You can currently achieve the same behavior by simply adding the id attribute to your DjangoObjectType class explicitly.

class MyObject(DjangoObjectType):
    foreign_id_one = graphene.ID()
    foreign_id_two = graphene.ID()

    class Meta:
        model = MyObjectModel

Usage after this PR

Turn on the setting

GRAPHENE = {
    ...
    'INCLUDE_FOREIGNKEY_IDS': True
}

Then DjangoObjectTypes are simple

class MyObject(DjangoObjectType):

    class Meta:
        model = MyObjectModel

And then you can simply do:

{
  myObjects {
    relatedObjectId
  }
}

And avoid making a join when you don't have to.

While the workaround isn't difficult, in a large project with lots of models and relations, it can be a lot to add. In our case, we want these IDs present on all models, so it makes sense to provide a more convenient approach.

[spockNinja]

@syrusakbary

Does this seem like a feature you'd like to include in this repo? If so, I'll add some tests and documentation. If not, I'll just implement it for our project's graphql wrappers and close this PR.

[coveralls]

Coverage decreased (-0.08%) to 92.645% when pulling 6d2e60e on spockNinja:feature/include-id-fields into 0588f89 on graphql-python:master.

[coveralls]

Coverage decreased (-0.08%) to 92.645% when pulling 6d2e60e on spockNinja:feature/include-id-fields into 0588f89 on graphql-python:master.

[coveralls]

Coverage decreased (-0.08%) to 92.645% when pulling 6d2e60e on spockNinja:feature/include-id-fields into 0588f89 on graphql-python:master.

[spockNinja]

I'm actually wondering if this would be nicer as a global setting? It's still a bit tedious to add that line to every DjangoObjectType Meta.

[coveralls]

Coverage increased (+0.04%) to 93.184% when pulling fc5655e on spockNinja:feature/include-id-fields into d7c160c on graphql-python:master.

[firaskafri]

@jkimbo @dopeboy @danpalmer
What do you think?

[phalt]

This is a cool feature but it feels like a use case that isn't general enough to add a whole setting for. Could this not just be done with resolver methods?

I'd like to tidy up some of the PRs, so if we still want to work on this let me know or I will close this in 1 week.