graphql

What is graphql?

The graphql npm package is the JavaScript reference implementation for GraphQL, a query language for APIs and a runtime for executing those queries by using a type system you define for your data. It allows you to create schemas, define resolvers, and execute GraphQL queries and mutations.

What are graphql's main functionalities?

Creating a GraphQL Schema

This feature allows you to define the shape of your data and the way it can be queried by clients. The code sample demonstrates how to create a simple GraphQL schema with a single root query.

const { GraphQLSchema, GraphQLObjectType, GraphQLString } = require('graphql');

const schema = new GraphQLSchema({
  query: new GraphQLObjectType({
    name: 'RootQueryType',
    fields: {
      hello: {
        type: GraphQLString,
        resolve() {
          return 'Hello world!';
        }
      }
    }
  })
});

Executing a GraphQL Query

This feature allows you to execute GraphQL queries against your schema. The code sample shows how to execute a simple query that asks for the 'hello' field, which resolves to 'Hello world!'.

const { graphql, buildSchema } = require('graphql');

const schema = buildSchema(`
  type Query {
    hello: String
  }
`);

const root = { hello: () => 'Hello world!' };

graphql(schema, '{ hello }', root).then((response) => {
  console.log(response);
});

Defining Resolvers

Resolvers are functions that resolve the value for a type or field in a schema. The code sample shows how to define a resolver for the 'hello' field that returns a string.

const { GraphQLObjectType, GraphQLString } = require('graphql');

const RootQueryType = new GraphQLObjectType({
  name: 'RootQuery',
  fields: {
    hello: {
      type: GraphQLString,
      resolve() {
        return 'Hello world!';
      }
    }
  }
});

Other packages similar to graphql

apollo-server

Apollo Server is a community-driven, open-source GraphQL server that works with many Node.js HTTP server frameworks. It simplifies building a GraphQL API by providing features like performance tracing and schema stitching. Compared to graphql, Apollo Server offers a more integrated set of tools for building production-ready GraphQL services.

express-graphql

Express GraphQL is a GraphQL HTTP server middleware for Express.js. It allows you to serve a GraphQL API as a web service. While graphql provides the core functionality for schema creation and query execution, express-graphql makes it easy to integrate GraphQL with the Express web application framework.

type-graphql

TypeGraphQL is a framework for building GraphQL APIs in Node.js using TypeScript, based on the official graphql-js package. It allows for defining the schema using TypeScript classes and decorators, which can be more familiar to developers with an object-oriented background. It provides a more type-safe and class-based approach to defining GraphQL schemas compared to the more traditional, function-based approach of graphql.

README

GraphQL.js

This is a technical preview of the JavaScript reference implementation for GraphQL, a query language created by Facebook for describing data requirements on complex application data models.

Technical Preview Contents

This technical preview contains a [draft specification for GraphQL] (https://github.com/facebook/graphql) and a reference implementation in JavaScript that implements that draft, GraphQL.js.

The reference implementation provides base libraries in JavaScript that would provide the basis for full GraphQL implementations and tools. It is not a fully standalone GraphQL server that a client developer could use to start manipulating and querying data. Most importantly, it provides no mapping to a functioning, production-ready backend. The only “backend” we have targeted for this early preview are in-memory stubs in test cases.

We are releasing this now because after GraphQL was first discussed publicly, many engineers used this information to implement the parts of the system that we discussed publicly. We want to support those engineers by providing both a formal specification and a reference implementation for the system as a whole.

To that end, the target audience is not the client developer, but those who have built or are actively interested in building their own GraphQL implementations and tools. Critically, we also want feedback on the system and to incorporate that feedback in our final release.

In order to be broadly adopted, GraphQL will have to target a wide variety of backends, frameworks, and languages, which will necessitate a collaborative effort across projects and organizations. This technical preview marks the beginning of that process.

Getting Started

An overview of GraphQL in general is available in the README for the Specification for GraphQL. That overview describes a simple set of GraphQL examples that exist as tests in this repository. A good way to get started with this repository is to walk through that README and the corresponding tests in parallel.

Using GraphQL.js

Install GraphQL.js from npm

npm install graphql

GraphQL.js provides two important capabilities: building a type schema, and serving queries against that type schema.

First, build a GraphQL type schema which maps to your code base.

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

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

This defines a simple schema with one type and one field, that resolves to a fixed value. A more complex example is included in the top level tests directory.

Then, serve the result of a query against that type schema.

var query = '{ hello }';

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

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

});

This runs a query fetching the one field defined. The graphql function will first ensure the query is syntactically and semantically valid before executing it, reporting errors otherwise.

var query = '{ boyhowdy }';

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

  // Prints
  // {
  //   errors: [
  //     { message: 'Cannot query field boyhowdy on RootQueryType',
  //       locations: [ { line: 1, column: 3 } ] }
  //   ]
  // }
  console.log(result);

});

Contributing

After cloning this repo, ensure dependencies are installed by running:

npm install

GraphQL is written in ES6 and uses Babel for ES5 transpilation and Flow for type safety. Widely consumable JavaScript can be produced by running:

npm run build

Once npm run build has run, you may import or require() directly from node.

After developing, the full test suite can be evaluated by running:

npm test

While actively developing, we recommend running

npm run watch

in a terminal. This will watch the file system run lint, tests, and type checking automatically whenever you save a js file.

To lint the JS files and type interface checks run npm run lint.