5. On the Server-Side - Creating Your First Schema.md

Part 5: On the server-side - Creating your first schema

We've learnt a great deal of how to prepare GraphQL queries. Let's dive into the next step- building a very simple GraphQL server.

The first step to build a working GraphQL API is providing a schema. The GraphQL engine will parse queries, then validate and return the data based on your designed type schema.

By design, GraphQL schemas are strongly typed. This gives the system a way to validate the query and guarantees the shape of the response.

Here's an example of a simple GraphQL schema that returns {hello: 'world'} for a {hello} query:

import {
  graphql,
  GraphQLSchema,
  GraphQLObjectType,
  GraphQLString
} from 'graphql';

var schema = new GraphQLSchema({
  query: new GraphQLObjectType({
    name: 'RootQueryType',
    fields: {
      hello: {
        type: GraphQLString,
        resolve: () => 'world'
      }
    }
  })
});

/* Dummy GraphQL query.
   In real-life we'll get it from the client side.
*/
var query = `
  query HelloQuery {
    { hello }
  }
`;

graphql(schema, query).then((result) => {
  // Prints
  // {
  //   data: { hello: "world" }
  // }
  console.log(result);
});

If you need to accept parameters to get results, that's easy too. We need to define what type of parameter we accept via an args object on fields, and pass that to the resolve function. Here's an updated version of the above sample that takes a greet parameter of GraphQLString type:

import {
  graphql,
  GraphQLSchema,
  GraphQLObjectType,
  GraphQLString
} from 'graphql';


var schema = new GraphQLSchema({
  query: new GraphQLObjectType({
    name: 'RootQueryType',
    fields: {
      hello: {
        type: GraphQLString,
        args: {
          greet: { type: GraphQLString }
        },
        //Using Destructuring feature of ES2015 to assign value to greet
        resolve: (root, {greet}) => {
          greet = greet ? greet + '!' : 'world!';
          return greet;
        }
      }
    }
  })
});

var query = `
  query Welcome {
    hello (greet: "mehdi")
  }
`;

graphql(schema, query).then((result) => {

  // Prints
  // {
  //   data: { hello: "mehdi!" }
  // }
  console.log(result);
});

Have you noticed that we are using double-quotes in hello (greet: "mehdi") in our query? That's because using single-quotes in GraphQLString type parameters is invalid. Tada!

If you are using server-side MVC frameworks like Ruby on Rails, Laravel or SailsJS, you are probably getting a hint here that the coming days are going to be a lot different with GraphQL. The V in MVC has already gone from the server-side in API only use cases. What's next? I can only speculate there will be rudimentary routing for our API servers, as we won't have a bunch of routes but a single endpoint. The schema will do a lot of validation for us, a lot of authentication & authorization will be on middleware layers, as they are now. The resolve function of the fields will probably take a lot of responsibility from controllers. The only least affected areas might be the models/ORM layer. Or maybe GraphQL will co-exists with REST and pre-dominant MVC style server-side architecture for a long time. I don't know. But I'm excited to embrace what's coming in the near future!

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