Graphql2rest-tmp NPM

GraphQL2REST

Automatically generate a RESTful API from your existing GraphQL API

GraphQL2REST is a Node.js library that reads your GraphQL schema and a user-provided manifest file and automatically generates an Express router with fully RESTful HTTP routes — a full-fledged REST API. npm.io

Why?

You have an existing GraphQL API, but need to expose it as REST because that's what your API users want
You want to develop a new GraphQL API and get REST on top of it, for free
You want to benefit from GraphQL internally while exposing REST externally as a public API

GraphQL2REST allows fully configuring and customizing your REST API, which may sit on top of a very different GraphQL layer (see features and advanced examples).

Installation

npm:

npm i graphql2rest

yarn:

yarn add graphql2rest

Usage

Basic example:

Given a simple GraphQL schema:

type Query {  
	getUser(userId: UUID!): User  
}  

type Mutation {
	createUser(name: String!, userData: UserDataInput): User
	removeUser(userId: UUID!): Boolean
}

Add REST endpoints to the manifest.json file:

{
	"endpoints": {
		"/users/:userId": {
			"get": {
				"operation": "getUser",
			},
			"delete": {
				"operation": "removeUser",
				"successStatusCode": 202
			}
		},
		"/users": {
			"post": {
				"operation": "createUser",
				"successStatusCode": 201
			}
		}
	}
}

In your code:

import GraphQL2REST from 'graphql2rest';
import { execute } from 'graphql'; // or any GraphQL execute function
import { schema } from './myGraphQLSchema.js' 

GraphQL2REST.generateGqlQueryFiles(schema, './gqlFilesFolder'); // a one time pre-processing step

const restRouter = GraphQLREST.init(schema, execute);

// restRouter now has our REST API attached
const app = express(); 
app.use('/api', restRouter);

Resulting API:

POST /api/users              --> 201 CREATED 
GET /api/users/{userId}      --> 200 OK 
DELETE /api/users/{userId}   --> 202 ACCEPTED

// Example:

GET /api/users/1234?x-filter=name,role 

Will invoke getUser query and return only 'name' and 'role' fields in the REST response. 
(the name of the filter query param is customizable).

For more examples and usage, please refer to the Tutorial.

Features

Use any type of GraphQL server - you provide the execute() function
Default "RESTful" logic for error identification, determining status codes and response formatting
Customize response format (and error responses format too, separately)
Custom parameter mapping (REST params can be different than GraphQL parameter names)
Customize success status codes for each REST endpoint
Map custom Apollo GraphQL error codes to HTTP response status codes
Map a single REST endpoint to multiple GraphQL operations, with conditional logic to determine mapping
Hide specific fields from responses
Run custom middleware function on incoming requests before they are sent to GraphQL
Client can filter on all fields of a response, in all REST endpoints, using built-in filter
Built-in JMESPath support (JSON query language) for client filter queries
GraphQL server can be local or remote (supports apollo-link and fetch to forward request to a remote server)
Embed your own winston-based logger

How GraphQL2REST works

GraphQL2REST exposes two public functions:

generateGqlQueryFiles() - GraphQL schema pre-processing
init() - generate Express router at runtime

First, GraphQL2REST needs to do some one-time preprocessing. It reads your GraphQL schema and generates .gql files containing all client operations (queries and mutations). These are "fully-exploded" GraphQL client queries which expand all fields in all nesting levels and all possible variables, per each Query or Mutation type.

This is achieved by running the generateGqlQueryFiles() function:

GraphQL2REST.generateGqlQueryFiles(schema, './gqlFilesFolder');

Now the ./gqlFilesFolder contains an index.js file and subfolders for queries and mutations, containing .gql files corresponding to GraphQL operations.

generateGqlQueryFiles() has to be executed just once, or when the GraphQL schema changes (it can be executed offline by a separate script or at "build time").

After generateGqlQueryFiles() has been executed once, GraphQL2REST init() can be invoked to create REST endpoints dynamically at runtime.

init() loads all .gql files into memory, reads the manifest.json file and uses Express router to generate REST endpoint routes associated with the GraphQL operations and rules defines in the manifest. init() returns an Express router mounted with all REST API endpoints.

The init() function

GraphQL2REST.init() is the entry point which creates REST routes at runtime.

It only takes two mandatory parameters: your GraphQL schema and the GraphQL server execute function (whatever your specific GraphQL server implementation provides, or an Apollo Link function).

GraphQL2REST.init(
	schema: GraphQLSchema, 
	executeFn: Function,
	
	options?: Object,
	formatErrorFn?: Function,
	formatDataFn?: Function,
	expressRouter?: Function)

options defines various settings (see below). If undefined, default values will be used.

formatErrorFn is an optional function to custom format GraphQL error responses.

formatDataFn is an optional function to custom format non-errror GraphQL responses (data). If not provided, default behavior is to strip the encapsulating 'data:' property and omit the 'errors' array from successful responses.

expressRouter is an express.Router() instance to attach new routes to (if not provided, a new Express instance will be returned) .

The Manifest File

REST API endpoints and their behavior are defined in the manifest file (normally manifest.json ). It is used to map HTTP REST routes to GraphQL operations and define error code mappings. See a full example here.

The `endpoints` section

The endpoints object lists the REST endpoints to generate:

"endpoints": {
	"/tweets/:id": {  // <--- HTTP route path; path parameters in Express notation
		"get": {      // <--- HTTP method (get, post, patch, put, delete) 
			"operation": "getTweetById", // <--- name of GraphQL query or mutation
		}
	}
}

Route path, HTTP method and operation name are mandatory.

GraphQL2REST allows mapping a single REST endpoint to multiple GraphQL operations by using an array of operations (operations[] array instead of the operation field).

Additional optional fields:

"params": Used to map parameters in the REST request to GraphQL arguments in the corresponding query or mutation. Allows renaming parameters so the REST API can use different naming than the underlying GraphQL layer. If omitted, parameters will be passed as is by default. [Learn more]
"successStatusCode": Success status code. If omitted, success status code will be 200 OK by default. [Learn more]
"condition": Conditions on the request parameters. GraphQL operation will be invoked only if the condition is satisfied. Condition is expressed using MongoDB query language query operators. [Learn more]
"hide": Array of fields in response to hide. These fields in the GraphQL response will always be filtered out in the REST response. [Learn more]
"wrapRequestBodyWith": Wrap the request body with this property (or multiple nested objects expressed in dot notation) before passing the REST request to GraphQL. Allows mapping the entire HTTP body to a specific GraphQL Input argument. Helpful when we want the REST body to be flat, but the GraphQL operation expects the input to be wrapped within an object. [Learn more]
"requestMiddlewareFunction": Name of a middleware function (in the middleware.js module) to call before passing the request to the GraphQL server. This function receives the express req object and returns a modified version of it. [Learn more]
Another example:

// Mutation updateUserData(userOid: UUID!, newData: userDataInput!): User 
// input userDataInput { name: String, birthday: Date } 
// type User { id: UUID!, name: String, birthday: Date, internalSecret: String }

"endpoints": {
	"/users/:id": {  
		"patch": {      
			"operation": "updateUserData",
			"params": {                       // <-- map or rename some params 
				"userOid": "id"               // <-- value of :id will be passed to userOid in mutation   
			},
			"successStatusCode": 202          // <-- customize success status code (202 is strange but valid)
			"wrapRequestBodyWith": "newData", // <-- allow flat REST request body
			"hide": ["internalSecret"] // <-- array of fields to omit from final REST response
		}
	}
}
// PATCH /users/{userId}, body = {"name": "Joe", "birthday": "1990-1-14"} 
// Response: 202 ACCEPTED 
// { "id": THE_USERID, "name": "Joe", "birthday": "1990-1-14"} // "internalSecret" omitted

The `errors` section

The optional “errors” object allows mapping Apollo GraphQL error codes to HTTP status codes, and adding an optional additional error message. The first error element in GraphQL's errors array is used for this mapping.

Example:

"errors": {
	"errorCodes": {
		"UNAUTHENTICATED": {
			"httpCode": 401,
			"errorDescription": "Forbidden: Unauthorized access",
		}
	}
}

In this example, responses from GraphQL which have an errors[0].extension.code field with the value "UNAUTHENTICATED" will produce a 401 Unauthorized HTTP status code, and the error description string above will be included in the JSON response sent by the REST router.

For GraphQL error codes that have no mappings (or if the "errors" object is missing from manifest.json), a 400 Bad Request HTTP status code will be returned by default for client errors, and a 500 Internal Server Error will be returned for errors in the server or uncaught exceptions.

Configuration

Settings can be configured in the options object provided to init(). For any fields not specified in the options object, or if options is not provided to init(), values from the defaults.json file will be used.

const gql2restOptions  = {
	apiPrefix: '/api/v2', //sets the API base path url 
	manifestFile: './api-v2-manifest.json', //pathname of manifest file  
	gqlGeneratorOutputFolder: './gqls', //.gql files folder (generated by generateGqlQueryFiles())
	middlewaresFile:  './middlewares.js', //optional middlewares module for modifying requests
	filterFieldName: 'fields', //global query parameter name for filtering (default is 'x-filter'),
	graphqlErrorCodeObjPath: 'errors[0].extensions.code', //property for Apollo error code upon error 
	logger: myCustomLogger //optional Winston-based logger function
};

const expressRouter = GraphQL2REST.init(schema, execute, gql2restOptions);

Use path.resolve(__dirname, <PATH>) for relative paths.

All fields in options are optional, but init() will not be able to run without a valid manifest file and gqlGeneratorOutputFolder previously populated by generateGqlQueryFiles().

Tutorial

Getting started
The manifest file - How parameters are passed - Mapping and renaming parameters - Success and error HTTP status codes - Hiding fields in REST responses - Mapping to GraphQL operations using conditional logic
Pre-processing step
Generating the REST API with init()
Using request middleware functions
Filtering and shaping the responses on the client side
Customizing and formatting response format
Using apollo-link to work with a remote GraphQL server

Running tests

npm test

Or, for tests with coverage:

npm run test:coverage

Benefits

GraphQL2REST allows creating a truly RESTful API that might be very different than the original, unchanged GraphQL API, without writing a single line of code.
The resulting REST API enjoys the built-in data validation provided by GraphQL due to its strong type system. Executing a REST API call with missing or incorrect parameters will automatically result in an informative error provided by GraphQL (which can be custom formatted to look like REST).
An old REST API can be migrated to a new GraphQL API gradually, by first building the GraphQL API and using GraphQL2REST to generate a REST API on top of it, seamlessly. That new REST API will have the same interface as the old one, and the new implementation can then be tested, endpoints migrated in stages, until a full migration to the underlying GraphQL API takes place.