lacinia-apollo-federation

A Clojure library allowing the creating of a schema which is compatible with Apollo's federation spec.

Usage

Imagine we have an toy movie schema:

schema {
  query: Query
}

type Query {
  Movie: [Movie!]
}

type Movie @key(fields: "id") {
  id: ID!
  title: String!
}

We've already added the @key directive to the Movie type as-per the spec.

Start out with a :require of com.atomist.lacinia-apollo-federation:

(ns my.app
  (:require [com.atomist.lacinia-apollo-federation :as federation]))

For each type the schema declares we'll need to register a resolve-reference (this is equivalent to Apollo's __resolveReference function). The following example registers a reference resolver for the :Movie type which we lookup by :id.

(defmethod federation/resolve-reference :Movie
  [reference]
  (fetch-movie-by-id (:id reference)))

Finally create your federated schema. At the moment the library only takes the raw SDL string form of the schema so pass it into build-federated-schema along with any resolvers required for this schema. The library will create the necessary additional schema elements required by the federation spec.

(def compiled-schema
  (-> "schema.graphql"
      io/resource
      slurp
      (federation/build-federated-schema {:resolvers {:Query {:Movie fetch-all-movies}}})
      schema/compile))