Querying a set of data

If we want to expand our REST API to allow for querying all of the users in our database, we need to add a new endpoint:

rest-server.js:

// Listen for all GET requests to /users
server.get('/users', (req, res) => {
  // Find all of the users in the database collection (we pass in
  // an empty collection as we aren't filtering the results)
  User.find({}, (err, users) => {
    if (err) {
      // The DB returned an error so we return a 500 error
      return res.status(500).end()
    }

    // Return the array of users to the client (automatically
    // serialized as a JSON string)
    res.send(users)
  })
})

Like before, we can do a GET request to the new /users endpoint to see the user data returned as an array of objects:

$ curl http://localhost:3000/users
[{"_id":"123","username":"jeresig"},{"_id":"456","username":"lorensr"}]

With our GraphQL endpoint, we can achieve a similar result by adding a users query to our schema:

type Query {
  user(id: String!): User
  users: [User]
}

And by adding an associated loader for that data, which is just a single function:

graphql-server.js

// The query fields that we'll use to get the data for our
// main queries
rootValue: {
  user({ id }) { … },
  // Get an array of users and return them as a Promise
  users() {
    return User.find({})
  }
},

And that’s all we need! The query syntax changes ever so slightly to make this new users query, but the rest of it stays intact. We still ask for the fields on the User type that we want, but we do so with the same syntax, even though we’re operating against a set of users (rather than a single object). The query:

query {
  users {
    _id
    username
  }
}

This is one of the beauties of GraphQL: it’s designed to scale easily from a single object to multiple with little change in our code. The result is as we would expect—it’s just an array of user objects on the "users" attribute.

{"data":{"users":[{"_id":"123","username":"jeresig"},{"_id":"456","username":"lorensr"}]}}

Now that we have the basics out of the way, let’s look at some of the advanced features of REST APIs that GraphQL makes trivial.