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Version: current

Falcon Server API

This section provides an API description for both packages - @deity/falcon-server and @deity/falcon-server-env


src/models/Extension is a base class for any extension that is being used by Falcon Server Application. It adds a few helpful methods to provide a seamless integration with Falcon Server applications.

async extension.getGraphQLConfig(typeDefs = '')

This method will be called by the ExtensionContainer to get Extension's GraphQL configuration, which will be merged with the rest of the extension configs (see example below).

When calling parent method in your derived class - you could optionally pass your typeDefs parameter (super.getGraphQLConfig(typeDefs)) - default implementation of this method will automatically bind your Query and Mutation types to your ApiDataSource methods (following the same names for field and methods).


By default, this method will trigger api.getFetchUrlPriority(url: string) method (if it was defined in the assigned ApiDataSource instance) and pass the current URL to determine API's priority (for sort order) when Falcon Client fetches URL info from available extensions; if such method was not defined - it will return null, meaning that this ApiDataSource does not support "Dynamic Routing" and should be skipped.

async extension.fetchUrl(obj, args, context, info)

This method is optional and should be defined if ApiDataSource supports Dynamic Routing. Its signature mimics GraphQL Resolver function signature (root, params, context, info).


The purpose of this class is to provide some essential tools and capabilities to work with the remote REST API backend implementing required methods for the target Extension.

Basic structure of a new ApiDataSource module could look like this:

const { ApiDataSource } = require('@deity/falcon-server-env');
class MyApi extends ApiDataSource {

ApiDataSource is the base class for REST API data sources that Falcon-Server needs for a proper data-flow and communication.

new ApiDataSource(params)

params is an object with the following structure:

  • name - an optional string parameter to set the name of your ApiDataSource
  • config - an optional config object for your class
    • host, port and protocol keys are checked automatically to build Base URL for your REST API backend
    • perPage (default 10) - is used to limit your listings to a certain amount
    • fetchUrlPriority (default 3, which equals to ApiUrlPriority.NORMAL) - statically set Fetch URL priority for Dynamic Route
  • eventEmitter - an instance of EventEmitter2 (passed automatically by ApiContainer)
  • apiContainer - an instance of ApiContainer class (passed automatically by ApiContainer)
  • gqlServerConfig an Apollo Server configuration object (passed automatically by DataSource callback on every request)
new ApiDataSource({
name: 'customApiName', // by default, ApiContainer will pass key string from the configuration
config: {} // "config" object that is defined in your server configuration


This method must be defined if a specific ApiDataSource supports Dynamic Routing. It should provide a simple logic to determine a custom priority or return a default one (this.fetchUrlPriority equals ApiUrlPriority.NORMAL by default).

async api.fetchUrl(obj, args, context, info)

This method must be defined if a specific ApiDataSource supports Dynamic Routing. It will be called whenever Dynamic Route chooses this ApiDataSource instance to resolve URL type for the provided path. See Dynamic Route result response type here.


This is an optional method to define Cache Context object for your ApiDataSource instance. If your API does not require any distinctive data to be checked while calculating a cache key - you can omit this method. Otherwise, if your API does require such data (like selected store or language which is being stored in the API DataSource session and not being exposed as an input variable) - you could add this method to your ApiDataSource class and return an object like below:

class MyCustomApi extends ApiDataSource {
getCacheContext() {
return {
storeCode: this.session.storeCode

async api.fetchBackendConfig(obj, args, context, info)

If defined, ExtensionContainer will call this method whenever somebody tries to fetch backendConfig GQL Query field. Falcon-Server expects fetchBackendConfig to return an object with an optional locales array (like: ['en_US', 'nl_NL']).

Falcon-Server will merge and return only those locales that are present in every extension that has fetchBackendConfig method defined. If extension provides backend config, but doesn't care about locales (does not return it in response) - Falcon-Server will skip it.

Hooks and methods

Request context

It is possible to pass a context data to a single request via init object (3rd argument) using context key for the following REST methods - get, post, patch, put and delete:

async getInfo() {
return this.get('info', {}, {
context: { // passing request-related context
foo: 'bar'

This context object will be passed to willSendRequest and resolveUrl methods so you could perform a context-specific changes to your request before it gets send:

protected async willSendRequest(request) {
const { context } = request;
if (context && context.foo === 'bar') {
// do something else...

isAuthRequired context hook

Base ApiDataSource class provides a small isAuthRequired hook by default. If your class defines authorizeRequest(req) method and you pass isAuthRequired context flag to any of the REST methods - ApiDataSource will call authorizeRequest method of your class before sending the actual request further:

async authorizeRequest(req) {
// GET `/info` will call this method before making the request
const { token} = this.config;
req.headers.set('Authorization', `Bearer ${token}`);
async getInfo() {
return this.get('info', {}, {
context: { // passing request-related context
isAuthRequired: true

didReceiveResult context hook

If you pass async context.didReceiveResult callback - it will be triggered right between parsing REST response and saving this response to the internal cache, so this way - you have full control what to store in the cache:

async getInfo() {
return this.get('info', {}, {
context: { // passing request-related context
didReceiveResult: result => {
// Do something useful with `result`
result.myName = result.my_name;
return result;

This hook comes in handy whenever you want to change response data before sending it back to GraphQL to match its result type.

processPagination helper method

api.processPagination(totalItems, currentPage = null, perPage = null) is an internal method that helps you to process and generate a proper "pagination" object, which is used by Pagination GraphQL type. It helps to calculate missing properties for you, like nextPage and prevPage.

Session getter/setter

ApiDataSource provides 2 simple shortcut methods to work with session data:

  • api.session as a getter - returns a "named" session value
  • api.session as a setter - sets a "named" session value

"named" session value is an object extracted from the main "session" data object, additionally each ApiDataSource session is separated by the key - its own name, this.context.session[this.name].

async getInfo() {
// same as: const { userId } = this.context.session[this.name]
const { userId } = this.session;
// same as: this.context.session[this.name] = {}
this.session = {};
return this.get(`info/${userId}`);

Using ApiDataSource together with Extension

Sample config:

"apis": {
"api-wordpress": {
"package": "@deity/falcon-wordpress-api",
"config": {
"host": "wp.host.com",
"protocol": "https",
"apiPrefix": "/blog-api",
"apiSuffix": "/wp/v2"
"extensions": {
"blog": {
"package": "@deity/falcon-blog-extension",
"config": {
"api": "api-wordpress"

Sample ApiDataSource class:

const { ApiDataSource } = require('@deity/falcon-server-env');
class WordpressApi extends ApiDataSource {
async getPost(obj, args, context, info) {
// Calling 'https://wp.host.com/blog-api/wp/v2/posts/<id>' endpoint
return this.get(`/post/${args.id}`);

Sample Extension class:

const { Extension } = require('@deity/falcon-server-env');
const typeDefs = `
type Post {
name: String
extend Query {
getPost(id: String!): Post
class BlogExtension extends Extension {
async getGraphQLConfig() {
// or simply call super.getGraphQLConfig method
// to auto-bind GQL Query types to API methods
// return super.getGraphQLConfig(typeDefs);
return {
schemas: [typeDefs],
resolvers: {
Query: {
getPost: (obj, args, context, info) =>
context.dataSources[this.api.name].getPost(obj, args, context, info)

ApiContainer and ExtensionContainer will do the rest of the job:

  • Creating instances of both classes
  • Assigning specified extension.config.api Instance to Extension
  • Generating, stitching and merging GraphQL Schema for FalconServer


The main purpose of ApiContainer is to store, initialize and manage all provided APIs from the configuration. It also collects REST endpoints, required by the API to handle requests in old-fashioned way (for example - processing payment callbacks).

new ApiContainer(eventEmitter)

The constructor expects to receive an instance of EventEmitter.

apiContainer.registerApis(apis: Object<string, ApiInstanceConfig>)

This method registers the provided APIs (ApiInstanceConfig) into apiContainer.dataSources Map. Constructor will create a new Map, so any further manual calls of registerApis method will add new API DataSources to it.

All endpoints that were collected from API DataSources will be stored in apiContainer.endpoints property.

ApiInstanceConfig type

  • package: string - Node package path (example: @deity/falcon-wordpress-api)
  • config: object - Config object to be passed to Api Instance constructor


The main purpose of ExtensionContainer is to store, initialize and manage all provided extensions from the configuration. It also generates main configuration object for ApolloServer instance.

new ExtensionContainer(eventEmitter)

The constructor expects to receive an instance of EventEmitter.

extensionContainer.registerExtensions(extensions: Object<string, ExtensionInstanceConfig>, dataSources: Map<string,ApiDataSource>)

list of objects and an initialized list of dataSources provided by ApiContainer.

This method registers the provided extensions (ExtensionInstanceConfig) into extensionContainer.extensions Map. Constructor will create a new Map, so any further manual calls of registerExtensions method will add new Extensions to it.

extension.api will be assigned automatically by registerExtensions method based on the provided configuration and dataSources value.

async initialize()

This method will be called by the FalconServer.start() method. It will initialize each registered extension.

async createGraphQLConfig(defaultConfig = {})

This method must return a valid ApolloServer configuration. This method will be called right before starting the ApolloServer instance, after initializing all the extensions and API DataSources.

ExtensionInstanceConfig type

  • package: string - Node package path (example: @deity/falcon-blog-extension)
  • config: object - Config object to be passed to Extension Instance constructor
  • config.api: string - API instance name to be used by the Extension

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