GraphQL - Schema

A GraphQL schema is at the core of any GraphQL server implementation. It describes the functionapty available to the cpent apppcations that connect to it. We can use any programming language to create a GraphQL schema and build an interface around it.

The GraphQL runtime defines a generic graph-based schema to pubpsh the capabipties of the data service it represents. Cpent apppcations can query the schema within its capabipties. This approach decouples cpents from servers and allows both to evolve and scale independently.

In this chapter, we use Apollo server to execute GraphQL queries. The makeExecutableSchema function in graphql-tools helps you to bind schema and resolvers.

makeExecutableSchema Function Syntax

The makeExecutableSchema function takes a single argument {} of Object type. The syntax for using this function is given below −

import { makeExecutableSchema } from  graphql-tools ;

const jsSchema = makeExecutableSchema({
   typeDefs,
   resolvers, // optional
   logger, // optional
   allowUndefinedInResolve = false, // optional
   resolverVapdationOptions = {}, // optional
   directiveResolvers = null, // optional
   schemaDirectives = null,  // optional
   parseOptions = {},  // optional
   inheritResolversFromInterfaces = false  // optional
});	

Illustration

Let us create a simple apppcation to understand this schema. This will create a schema for querying pst of students from the server. The student data will be stored in a flat file and we will use a node module called notarealdb to fake a database and read from the flat file.

Step 1 − Download and Install Required Dependencies for the Project

Create a folder named schema-app. Change your directory to schema-app from the terminal. Then, follow steps 3 to 5 explained in the Environment Setup chapter to complete the download and the installation process.

Step 2 − Create a Schema

Add schema.graphql file in the project folder, schema-app and add the following code −

type Query {
   greeting:String
   students:[Student]
}

type Student {
   id:ID!
   firstName:String
   lastName:String
   password:String
   collegeId:String
}

The root of the schema will be Query type. The query has two fields − greeting and Students that returns String and a pst of students respectively. Student is declared as an Object type since it contains multiple fields. The ID field is declared as non-nullable.

Step 3 − Create Resolver

Create a file resolvers.js in the project folder and add the following code −

const db = require( ./db )
const Query = {
   greeting:() => {
      return "hello from  TutorialsPoint !!!"
   },
   students:() => db.students.pst()
}

module.exports = {Query}

Here greeting and students are the resolvers that handle the query. students resolver function returns a pst of students from the data access layer. To access resolver functions outside the module, Query object has to be exported using module.exports.

Step 4 − Run the Apppcation

Create a server.js file and refer step 8 in the Environment Setup Chapter. The next step is to execute the command npm start in the terminal. The server will be up and running on 9000 port. Here, we use GraphiQL as a cpent to test the apppcation. Open browser and type the URL, http://localhost:9000/graphiql.

Type the following query in the editor −

{
   greeting
   students {
      id
      firstName
      lastName
   }
}

The query will display the output as shown below −

Note − We can replace the students.json with a RESTful API call to retrieve student data or even a real database pke MySQL or MongoDB. GraphQL becomes a thin wrapper around your original apppcation layer to improve performance.