Hydra Core

Hydra Core provides basic objects to work with Hydra enabled Web APIs.

Usage

Node.js

hydra-core is available on npm, to install it run:

npm install hydra-core

In the code, import hydra-core:

var hydra = require('hydra-core');

Examples

The examples folder contains working example code for the Hydra Issue Tracker Demo application.

cd examples
node api-demo.js 

An alternative example code uses the object model to access the Hydra Issue Tracker Demo application.

cd examples
node api-demo-model.js

API

hydra.Api

classes:

Array of hydra.Class objects defined in the API documentation.

operations:

Array of hydra.Operation objects defined in the API documentation.

findClass(iri):

Returns a hydra.Class object for the given IRI or undefined if the IRI is unknown.

findOperation(iri):

Returns a hydra.Operation object for the given IRI or undefined if the IRI is unknown.

hydra.Document

classes

Array of hydra.ClassDocument objects based on rdf:type triples in the document.

properties

Array of hydra.PropertyDocument objects based on triples in the document.

findOperation([propertyIri], method):

Returns a hydra.OperationDocument object or undefined if the operation was not found. Searches only in the classes of the document, if only the method argument is given. Searches for operations assigned to the property, if the propertyIri arguments is also given.

findProperty

Returns a hydra.PropertyDocument object for the given IRI or undefined if the IRI is unknown.

hydra.Class

hydra.ClassDocument

hydra.Operation

hydra.OperationDocument

hydra.Property

hydra.PropertyDocument

hydra.api(json, base)

Parses the given JSON-LD object or string and returns a hydra.Api object using a Promise. The base parameter is used to expand the given JSON-LD object.

hydra.document(api, json, base)

Parses the given JSON-LD object or string and returns a hydra.Document object using a Promise. api must be an instance of hydra.Api. The base parameter is used to expand the given JSON-LD object.

API Model

The hydra core object model uses JSON-LD objects extended with functions and additional @ properties. Hydra operations are mapped into the objects with the @ + lower case the HTTP method keys. For example, if an entry point class contains http://schema.org/blogPost property that implements a HTTP POST method to create a new blog post, the following code could be used:

// load the entry point from http://example.com/
hydra.model.load('http://example.com/')
  .then(function (entryPoint) {
    // create a new blog post using the post method of http://schema.org/blogPost
    return entryPoint['http://schema.org/blogPost']['@post']({
      'http://schema.org/name': 'blog post name',
      'http://schema.org/articleBody': 'this is the content of the blog post'
    });
  })
  .then(function (blogPost) {
    // write the IRI of the created blog post to the console
    console.log(blogPost['@id']);
  });

If a JSON-LD context is defined, the objects will be compacted using that context:

// define the context in the properties object, that will be merged into the model object 
hydra.model.load('http://example.com/', {'@context': {'@vocab': 'http://schema.org'}})
  .then(function (entryPoint) {
    // works also with the POST operation
    return entryPoint.blogPost['@post']({
      '@context': {'@vocab': 'http://schema.org'},
      name: 'blog post name',
      articleBody: 'this is the content of the blog post'
    }, {'@context': {'@vocab': 'http://schema.org'}});
  });

It's possible to add properties to the model object and hide them from the serialization. A @omit: true key value pair must be added to the property. The hydra.model.hide method can be used for this:

// assign a new hidden variable
blogPost.privateVariable = hydra.model.hide(privateVariable);

Every model object built with hydra.model.create contains a hidden variable api that contains the API documentation. That object can be used to create model objects based on classes defined in the API documentation:

hydra.model.create(entryPoint.api.findClass('http://schema.org/BlogPost'))
  .then(function (blogPost) {
  });

hydra.model.create(classes, properties, options)

Creates a model object bases on a single or an Array of hydra.Class or hydra.ClassDocument. The properties object is merged into the model object. Additional options that control the model object building.

hydra.model.hide(property)

Adds a @omit: true key value pair to the property object and returns that property object. property must be an object.

hydra.model.load(url, properties, options)

Creates a model object based on the result of a GET request to the given url. The properties and options arguments will be forwarded to the hydra.model.create function.

hydra.model.toJSON()

A toJSON function that removes all functions and properties that contain a @omit: true key value pair.