[Improvement in docs] Plugin Federation

[CyrilBLA]

Federation schema

In order for the queries to merge properly with fastify and mercurius gateway it's better to add in each subschema :

import SchemaBuilder from '@pothos/core';
import DirectivesPlugin from '@pothos/plugin-directives';
import FederationPlugin from '@pothos/plugin-federation';

const builder = new SchemaBuilder<{
  DefaultFieldNullability: true;
  FederationPolicies: 'user:policy';
}>({
  plugins: [DirectivesPlugin, FederationPlugin],
  directives: {
    useGraphQLToolsUnorderedDirectives: true,
  },
});

builder.queryType({
  directives: {
    extends: true,
  },
});

export const schema = builder.toSubGraphSchema({
  linkUrl: 'https://specs.apollo.dev/federation/v2.5',
  federationDirectives: ['@extends'],
});

With this on, schemas will merge perfectly on the gateway endpoint.

Shouldn't it be great to have it documented or put in the example ?

[hayes]

I think this makes sense. I haven't used federation myself, and am unfamiliar with the fastify implementation, but PRs to improve the docs (or the plugin itself) to make it easier to use are more than welcome!

The implementation here was mostly based on apollos compatibility test suite, which obviously is optimized for a specific implementation