gateway-custom-schema

API Gateway (Custom Schema)

Overview

This directory contains an example implementation for an API gateway on top of a Graphcool CRUD API. The idea is to customize the API operations that are exposed to your clients by hiding the original CRUD API and defining a custom schema on top of it.

The API gateway uses dedicated tooling that allows to easily implement a mapping from the custom schema to the underlying CRUD API.

Try out the read-only demo.

Get started

1. Download the example

curl https://codeload.github.com/graphcool/graphcool/tar.gz/master | tar -xz --strip=2 graphcool-master/examples/gateway-custom-schema
cd gateway-custom-schema

2. Install the Graphcool CLI

If you haven't already, go ahead and install the Graphcool CLI:

npm install -g graphcool@next

3. Deploy the Graphcool service

The next step is to deploy the Graphcool service that's defined inside the service directory:

cd service
graphcool deploy

When prompted which cluster you'd like to deploy, chose any of Backend-as-a-Service-options (shared-eu-west-1, shared-ap-northeast-1 or shared-us-west-2) rather than local.

Then copy the endpoint for the Simple API, you'll need it in the next step.

The service you just deployed provides a CRUD API for the User and Post model types that are defined in ./service/types.graphql.

The goal of the gateway server is now to create a custom GraphQL API that only exposes variants of the underlying CRUD API.

4. Configure and start the API gateway server

4.1. Set the endpoint for the GraphQL CRUD API

You first need to connect the gateway to the CRUD API.

Paste the the HTTP endpoint for the Simple API from the previous step into ./gateway/index.ts as the value for endpoint, replacing the current placeholder __SIMPLE_API_ENDPOINT__:

const endpoint = '__SIMPLE_API_ENDPOINT__' // looks like: https://api.graph.cool/simple/v1/__SERVICE_ID__

Note: If you ever lose your API endpoint, you can get access to it again by running graphcool info in the root directory of your service (where graphcool.yml is located).

4.2. Start the server

Navigate into the gateway directory, install the node dependencies and start the server:

cd ../gateway
yarn install
yarn start

4.3. Open GraphQL Playground

The API that's exposed by the gateway is now available inside a GraphQL Playground under the following URL:

http://localhost:3000/playground

Usage

1. Create dummy data using the CRUD API

Before you start running queries against the API gateway, you should create somme dummy data in your service's database. You'll do this with a GraphQL Playground that's running against the CRUD API (not the API gateway).

Navigate back into the service directory and open a Playground:

cd ../server
graphcool playground

In the Playground, send the following mutation to create a new User node along with three Post nodes:

mutation {
  createUser(
    name: "John", 
    alias: "john", 
    posts: [
      { title: "GraphQL is awesome" }, 
      { title: "Declarative data fetching with GraphQL" },
      { title: "GraphQL & Serverless" }
    ]
  ) {
    id
  }
}

Note: It's important the alias of the User is set to john. Otherwise the API gateway won't return any data since the alias in this example is hardcoded.

2. Send queries to the API gateway

Now, that there's some initial data in the database, you can use the API gateway to fetch the data through the exposed API. Note that these queries have to be run in the Playground that's running on your localhost: http://localhost:3000/playground.

Send the following query to fetch the posts that you just created:

{
  viewer {
    me {
      id
      name
      posts(limit: 2) {
        title
      }
    }
  }
}

What's in this example?

The API gateway is a thin layer on top of the Graphcool service's CRUD API. For this example, the CRUD API is based on the following data model defined in the service's types.graphql:

type User @model {
  id: ID! @isUnique
  name: String!
  alias: String! @isUnique
  posts: [Post!]! @relation(name: "UserPosts")
}

type Post @model {
  id: ID! @isUnique
  title: String!
  author: User! @relation(name: "UserPosts")
}

Everyone who has access to the HTTP endpoint of the CRUD API can see that it exposes the following operations:

type Query {
  # Read operations for `Post`
  Post(id: ID): Post
  allPosts(filter: PostFilter, orderBy: PostOrderBy, skip: Int, after: String, before: String, first: Int, last: Int): [Post!]!

  # Read operations for `User`
  User(alias: String, id: ID): User
  allUsers(filter: UserFilter, orderBy: UserOrderBy, skip: Int, after: String, before: String, first: Int, last: Int): [User!]!
}

type Mutation {
  # Create, update, delete operations for `Post`
  createPost(title: String!, authorId: ID, author: PostauthorUser): Post
  updatePost(id: ID!, title: String, authorId: ID, author: PostauthorUser): Post
  deletePost(id: ID!): Post

  # Create, update, delete operations for `User`
  createUser(alias: String!, name: String!, postsIds: [ID!], posts: [UserpostsPost!]): User
  updateUser(alias: String, id: ID!, name: String, postsIds: [ID!], posts: [UserpostsPost!]): User
  deleteUser(id: ID!): User

  # Set relation between `Post` and `User` node
  addToUserPosts(postsPostId: ID!, authorUserId: ID!): AddToUserPostsPayload
}

The API gateway now creates another API that will be exposed to the clients. The server that exposes this API is executing its queries against the underlying CRUD API. The magic enabling this functionality is implemented in the run function in index.ts.

Here's the schema that defines the new API:

type Query {
  viewer: Viewer!
}

type Viewer {
  me: User
  topPosts(limit: Int): [Post!]!
}

There are four major steps that are being performed to map the CRUD API to the new schema:

1. Create local version of the CRUD API using makeRemoteExecutableSchema. See the code.
2. Define schema for the new API (the one exposed by the API gateway). See the code.
3. Merge remote schema with new schema using mergeSchemas. See the code.
4. Limit exposed operations from merged schemas (hiding all root fields except viewer) using transformSchema. See the code.