Federation support

[hnrklssn]

Is there any plan to support Apollo Federation?

[jregistr]

Hi!
For something like this it'd make sense for it to be a package, similar to what we do already for Relay.

Speaking of which, in the next few weeks I'm going to start some chatter in this repo on a draft I'm working on.

[danestig]

I'm also interested in this and would be happy to contribute.

I've done some experimentation and the the main issue I'm facing is the _entities resolver. Currently it looks like this:

implicit ctx => Action.sequence[Ctx, Option[Any]](ctx.arg[Seq[JsValue]]("representations").map(getEntity))

and getEntity has this signature:

def getEntity(data: JsValue)(implicit ctx: Context[Ctx, _]): LeafAction[Ctx, Option[Any]]

This works as long as I don't have any DeferredValues, if I do, I run in to this issue #465.

[joshjones95]

Hi,

Has there been any discussions or packages that have started to support this for sangria?

[paulpdaniels]

It is possible to do, we have an internal implementation of it that we use for our services. The main issue that the marshallers need to be changed to support object scalars.

[yanns]

@paulpdaniels we would also be interested in that.
As far as I can understand you, it's not possible to support federation with a "simple" library.
Some more deeper changes are needed?

[paulpdaniels]

@yanns The spec itself is purely additive and can be put on top of the existing implementation. You need to add some new directives and probably some sugar to make them easy to add. But then the only change is that you need to basically wrap your existing schema with something like:

def federate[Ctx, Val: ClassTag](_schema: Schema[Ctx, Val], resolvers: EntityResolver[Ctx]*): Schema[Ctx, Val]

Where EntityResolver looks something like this:

trait EntityResolver[Ctx] {
  def typename: String

  def resolve(obj: JsObject): LeafAction[Ctx, Option[Any]]
}

I'll see if I can extract a gist of what we are doing. The incompatibility comes from the fact that the existing marshallers won't support the _Any scalar that federation needs. So we had to forked our own, basically: here and here need to be amended to accept the ObjectNode of the marshaller.

[paulpdaniels]

Here we go: https://gist.github.com/paulpdaniels/f6e637d1bbbd67d13ec661a7306e6af4

[danestig]

I've been using the same approach but I'm running into this #465 when the entity resolver doesn't return a deferred value but the entity has has nested deferred fields. Currently I'm resolving all entities to DeferredValues instead of LeafActions to work around this.

Other than that this is working well for me.

[paulpdaniels]

Interesting, haven't encountered that @ErikHedblom , though we still have a relatively small interplay of our federated services. Yeah the LeafAction is decidedly not great, there is probably someway to improve that syntax but will need some work on the internals I think.

[yanns]

Should I create a new repo under the sangria organization for that?
We could mark the library as "alpha" first.

[danestig]

I think that would be great, we should be able to use @paulpdaniels gist for the first version.

[zvuki]

👋 Is there any progress in this area?

[yanns]

You can find the first implementation here: https://github.com/sangria-graphql/sangria-federated/
Please use it with caution and provide feedback.