HalCrawler

Introduction

HAL Crawler is a client for consuming any API which is HAL (HATEOAS) compliant. Have a look at the spec of HALSpec if you're not familiar with it.

This library should be used in combination with a wrapper. For Redux there is an implementation halux.

Also have a look at the examples which provide pretty good information about the features of the HalCrawler as well as a sample integration with halux.

Schemas

Schemas define the data structure

new Schema(identifier: string, identifiers: string[] or schemaType, actionsWhichCanBePerformedOnInstance: action[], children: Schema[])

import { createConfig, crawl, Command, Schema, Resource, action } from "hal-crawler";
const admins = new Schema("ea:admin", ["id"], [action.GET]);
const orders = new Schema("ea:order", ["nested.id"], [action.GET]);

// [] => list of resources, if only one can occur the [] can be removed
const root = new Schema("root", [], [action.GET], [[admins], [orders]]);
// e.g.:
const clients = new Schema("clients", [], [action.GET], [[client], mostImportantClient]);

Note that instead of identifiers you can also define special schemaTypes using the schemaType: const foods = new Schema("foods", schemaType.linkIdentifiedResource); There are two schemaTypes: linkIdentifiedResource -> this resource can only be identified using the self link singleInstanceResource -> there is only one instance of this resource

configuration

the crawler needs some basic information, this must be passed using configuration objects, only the root resource is mandatory, fetchOptions are also possible. Consult whatwg-fetch to see what options can be passed to fetch().

const config = createConfig({
  root: "root.json",
  fetchOptions: {
    // these options will be passed directly to whatwg-fetch()
  }
});

Resource

A resource represents data from an endpoint. There are different kinds of resources:

• Full Resource: contains all links, data
• Shallow Link Resource: contains only the link to itself (used by crawl and getResourceFromStore)
• Shallow identifiers Resource: contains only the identifiers (used by getResourceFromStore)

new Resource(root, [link], [data]);

In order to get child links of a resource use the getChildLink(schema) helper. This returns the link or an array of links which is available on a resource.

In order to get child data of a resource use the getChildData(schema) helper. This returns the data or an array of data which is available on a resource.

Command

a command defines an action which should be performed on a given resource. The resource as well as the action is mandatory

new Command(Resource, action.GET);

Only for the root resource action is not required

new Command(new Resource(root));

crawl

crawl is the main API, it executes a given command

crawl(config, new Command(new Resource(root))).then(store => {
  const rootInstance = getResourceFromStore(store, new Resource(root));
  const adminLinks = rootInstance.getChildLink(admins);

  crawl(config, new Command(new Resource(admins, adminLinks[0]), action.GET), store).then(store => {
    console.log(getResourceFromStore(store, new Resource(admins, undefined, {id: 2})));
  });

  const orderLinks = rootInstance.getChildLink(orders);

  crawl(config, new Command(new Resource(orders, orderLinks[0]), action.GET), store).then(store => {
    console.log(getResourceFromStore(store, new Resource(orders, undefined, {id: 2})));
  });
});

getResourceFromStore

getResourceFromStore is responsible for retrieving a resource from the store, it accepts shallow link resources as well as shallow identifier resources.

getResourceFromStore(store, shallowResourceInstance);