graphql-composition

An implementation of GraphQL federated schema composition.

Example

use graphql_composition::{Subgraphs, compose, render_federated_sdl};

let user_subgraph = r#"
  extend schema
    @link(url: "https://specs.apollo.dev/federation/v2.3",
          import: ["@key"])

  type Query {
    findUserByEmail(email: String!): User
  }

  type User @key(fields: "id") {
    id: ID!
    name: String!
  }
"#;

let cart_subgraph = r#"
  extend schema
    @link(url: "https://specs.apollo.dev/federation/v2.3",
          import: ["@key", "@shareable"])

  type User @key(fields: "id") {
    id: ID!
    cart: Cart
  }

  type Cart @shareable {
    items: [String!]!
  }
"#;

let mut subgraphs = Subgraphs::default();

subgraphs.ingest_str(&user_subgraph, "users-service", "http://users.example.com").unwrap();
subgraphs.ingest_str(&cart_subgraph, "carts-service", "http://carts.example.com").unwrap();

let composed = compose(&subgraphs).into_result().unwrap();
let composed = render_federated_sdl(&composed).unwrap();

let expected = r#"
directive @core(feature: String!) repeatable on SCHEMA

directive @join__owner(graph: join__Graph!) on OBJECT

directive @join__type(
    graph: join__Graph!
    key: join__FieldSet
    resolvable: Boolean = true
) repeatable on OBJECT | INTERFACE

directive @join__field(
    graph: join__Graph
    requires: join__FieldSet
    provides: join__FieldSet
) on FIELD_DEFINITION

directive @join__graph(name: String!, url: String!) on ENUM_VALUE

directive @join__implements(graph: join__Graph!, interface: String!) repeatable on OBJECT | INTERFACE

directive @join__unionMember(graph: join__Graph!, member: String!) repeatable on UNION

scalar join__FieldSet

enum join__Graph {
    USERS_SERVICE @join__graph(name: "users-service", url: "http://users.example.com")
    CARTS_SERVICE @join__graph(name: "carts-service", url: "http://carts.example.com")
}

type User
    @join__type(graph: USERS_SERVICE, key: "id")
    @join__type(graph: CARTS_SERVICE, key: "id")
{
    cart: Cart @join__field(graph: CARTS_SERVICE)
    id: ID!
    name: String! @join__field(graph: USERS_SERVICE)
}

type Cart
    @join__type(graph: CARTS_SERVICE)
{
    items: [String!]!
}

type Query
{
    findUserByEmail(email: String!): User @join__field(graph: USERS_SERVICE)
}
  "#;

assert_eq!(expected.trim(), composed.trim());

Features

• The output is a structured, serializable format with all relevant relationships (FederatedGraph).
• FederatedGraph can be rendered to GraphQL SDL (see the example above).
• Good composition error messages.

Status

The crate is being actively developed and maintained.