GraphQL is a data query language and runtime designed and used at Facebook to request and deliver data to mobile and web apps since 2012.

Build a simple GraphQL server

If you don’t have node js already installed you can Install & run your first application Nodejs. We start by making a folder for our application:

    $ mkidr graph-server
    $ cd graph-server

Install graphql, express and express-graphql.

    $ npm install graphql 
    $ npm install express 
    $ npm install express-graphql

Create users.json Json file for Data

Create a file and name it users.json

    {
        "1": {
            "id": "1",
            "name": "Malekbenz",
            "email": "[email protected]"
        },
        "2": {
            "id": "2",
            "name": "user",
            "email": "[email protected]"
        },
        "3": {
            "id": "3",
            "name": "otheruser",
            "email": "[email protected]"
        },
        "4": {
            "id": "4",
            "name": "Superuser",
            "email": "[email protected]"
        }
    }

Create the Server

Create a file and name it app.js

    var graphql = require('graphql'),
        graphqlHTTP = require('express-graphql'),
        express = require('express');

// Import the users file
var users = require('./users.json');

// Define the User type. The type of User is GraphQLObjectType

var userType = new graphql.GraphQLObjectType({
  name: 'User',
  fields: {
    id: { type: graphql.GraphQLString },
    name: { type: graphql.GraphQLString },
    email: { type: graphql.GraphQLString },
  }
});

// Define the schema with one top-level field, 'user', that
// takes an 'id' argument and returns the User with that ID.

var schema = new graphql.GraphQLSchema({
  query: new graphql.GraphQLObjectType({
    name: 'Query',
    fields: {
      user: {
        type: userType,
        // 'args' arguments that the 'user' query accepts
        args: {
          id: { type: graphql.GraphQLString }
        },
        // The resolve function take 'id' argument from above as a key
        // to get the User from 'users'
        resolve: function (_, args) {
          return users[args.id];
        }
      }
    }
  })
});

express()
  .use('/graphql', graphqlHTTP({ schema: schema, pretty: true }))
  .listen(3000);

console.log('Server running on http://localhost:3000/graphql');

Save the file and run the application

    $ node app.js 

The server is running at localhost:3000/graphql. If you navigate to this address you will receive this notice:

 {
  "errors": [
    {
      "message": "Must provide query string."
    }
  ]
}

This message indicate that we need to provide a query.

Using a Queries againste a schema

A query is a string interpreted by a server that returns data in a specified format. Here is an example query:

Query:

{
  user(id: "1") {
    name
  }
}

Result:

{
  "data": {
    "user": {
      "name": "malekbenz"
    }
  }
}

Query:

{
  user(id: "2") {
    name,email
  }
}

Result:

{
  "data": {
    "user": {
      "name": "user",
      "email":"[email protected]"
    }
  }
}

You can edit the above query; the result will automatically update when you do. If you make a syntax mistake it will be underlined in red. Try replacing id: “1” with id: “2”; replace name with id or with name id.

Remove all the whitespace in the query: {user(id:"1"){name}} (whitespace is optional in GraphQL). You can send this to your server via a GET request with a URL query string: http://localhost:3000/graphql?query={user(id:”1”){name}} - the server should respond with

Congratulations! You’ve built your first GraphQL server. Try different queries, or changing the data, or even adding new fields to the schema.