# angular.service.$resource

Work in Progress This page is currently being revised. It might be incomplete or contain inaccuracies.

## Description

A factory which creates a resource object that lets you interact with RESTful server-side data sources.

The returned resource object has action methods which provide high-level behaviors without the need to interact with the low level `$xhr` service or raw XMLHttpRequest.

## Dependencies

- `$xhr.cache`

## Usage

    $resource(url[, paramDefaults][, actions]);

### Parameters

- `url – {string} –`

  A parameterized URL template with parameters prefixed by `:` as in `/user/:username`.

- `paramDefaults(optional) – {Object} –`

  Default values for `url` parameters. These can be overridden in `actions` methods.

  Each key value in the parameter object is first bound to url template if present and then any excess keys are appended to the url search query after the `?`.

  Given a template `/path/:verb` and parameter `{verb:'greet', salutation:'Hello'}` results in URL `/path/greet?salutation=Hello`.

  If the parameter value is prefixed with `@` then the value of that parameter is extracted from the data object (useful for non-GET operations).

- `actions(optional) – {Object.<Object>} –`

  Hash with declaration of custom action that should extend the default set of resource actions. The declaration should be created in the following format:

      {action1: {method:?, params:?, isArray:?, verifyCache:?},
       action2: {method:?, params:?, isArray:?, verifyCache:?},
       ...}

  Where:

  - `action` â {string} â The name of action. This name becomes the name of the method on your resource object.
  - `method` â {string} â HTTP request method. Valid methods are: `GET`, `POST`, `PUT`, `DELETE`, and `JSON` (also known as JSONP).
  - `params` â {object=} â Optional set of pre-bound parameters for this action.
  - isArray â {boolean=} â If true then the returned object for this action is an array, see `returns` section.
  - verifyCache â {boolean=} â If true then whenever cache hit occurs, the object is returned and an async request will be made to the server and the resources as well as the cache will be updated when the response is received.

### Returns

`{Object}` –

A resource "class" object with methods for the default set of resource actions optionally extended with custom `actions`. The default set contains these actions:

    { 'get':    {method:'GET'},
      'save':   {method:'POST'},
      'query':  {method:'GET', isArray:true},
      'remove': {method:'DELETE'},
      'delete': {method:'DELETE'} };

Calling these methods invoke an `angular.service.$xhr` with the specified http method, destination and parameters. When the data is returned from the server then the object is an instance of the resource class `save`, `remove` and `delete` actions are available on it as methods with the `$` prefix. This allows you to easily perform CRUD operations (create, read, update, delete) on server-side data like this:

          var User = $resource('/user/:userId', {userId:'@id'});
          var user = User.get({userId:123}, function(){
            user.abc = true;
            user.$save();
          });

It is important to realize that invoking a $resource object method immediately returns an empty reference (object or array depending on `isArray`). Once the data is returned from the server the existing reference is populated with the actual data. This is a useful trick since usually the resource is assigned to a model which is then rendered by the view. Having an empty object results in no rendering, once the data arrives from the server then the object is populated with the data and the view automatically re-renders itself showing the new data. This means that in most case one never has to write a callback function for the action methods.

The action methods on the class object or instance object can be invoked with the following parameters:

- HTTP GET "class" actions: `Resource.action([parameters], [success], [error])`
- non-GET "class" actions: `Resource.action(postData, [parameters], [success], [error])`
- non-GET instance actions: `instance.$action([parameters], [success], [error])`

## Example

### Credit card resource

         // Define CreditCard class
         var CreditCard = $resource('/user/:userId/card/:cardId',
          {userId:123, cardId:'@id'}, {
           charge: {method:'POST', params:{charge:true}}
          });

         // We can retrieve a collection from the server
         var cards = CreditCard.query();
         // GET: /user/123/card
         // server returns: [ {id:456, number:'1234', name:'Smith'} ];

         var card = cards[0];
         // each item is an instance of CreditCard
         expect(card instanceof CreditCard).toEqual(true);
         card.name = "J. Smith";
         // non GET methods are mapped onto the instances
         card.$save();
         // POST: /user/123/card/456 {id:456, number:'1234', name:'J. Smith'}
         // server returns: {id:456, number:'1234', name: 'J. Smith'};

         // our custom method is mapped as well.
         card.$charge({amount:9.99});
         // POST: /user/123/card/456?amount=9.99&charge=true {id:456, number:'1234', name:'J. Smith'}
         // server returns: {id:456, number:'1234', name: 'J. Smith'};

         // we can create an instance as well
         var newCard = new CreditCard({number:'0123'});
         newCard.name = "Mike Smith";
         newCard.$save();
         // POST: /user/123/card {number:'0123', name:'Mike Smith'}
         // server returns: {id:789, number:'01234', name: 'Mike Smith'};
         expect(newCard.id).toEqual(789);

The object returned from this function execution is a resource "class" which has "static" method for each action in the definition.

Calling these methods invoke `$xhr` on the `url` template with the given `method` and `params`. When the data is returned from the server then the object is an instance of the resource type and all of the non-GET methods are available with `$` prefix. This allows you to easily support CRUD operations (create, read, update, delete) on server-side data.

         var User = $resource('/user/:userId', {userId:'@id'});
         var user = User.get({userId:123}, function(){
           user.abc = true;
           user.$save();
         });

    It's worth noting that the success callback for `get`, `query` and other method gets passed
    in the response that came from the server, so one could rewrite the above example as:

         var User = $resource('/user/:userId', {userId:'@id'});
         User.get({userId:123}, function(u){
           u.abc = true;
           u.$save();
         });

### Buzz client

Let's look at what a buzz client created with the `$resource` service looks like:

           <script>
             function BuzzController($resource) {
               this.Activity = $resource(
                 'https://www.googleapis.com/buzz/v1/activities/:userId/:visibility/:activityId/:comments',
                 {alt:'json', callback:'JSON_CALLBACK'},
                 {get:{method:'JSON', params:{visibility:'@self'}}, replies: {method:'JSON', params:{visibility:'@self', comments:'@comments'}}}
               );
             }

             BuzzController.prototype = {
               fetch: function() {
                 this.activities = this.Activity.get({userId:this.userId});
               },
               expandReplies: function(activity) {
                 activity.replies = this.Activity.replies({userId:this.userId, activityId:activity.id});
               }
             };
             BuzzController.$inject = ['$resource'];
           </script>

           <div ng:controller="BuzzController">
             <input name="userId" value="googlebuzz"/>
             <button ng:click="fetch()">fetch</button>
             <hr/>
             <div ng:repeat="item in activities.data.items">
               <h1 style="font-size: 15px;">
                 <img src="{{item.actor.thumbnailUrl}}" style="max-height:30px;max-width:30px;"/>
                 <a href="{{item.actor.profileUrl}}">{{item.actor.name}}</a>
                 <a href ng:click="expandReplies(item)" style="float: right;">Expand replies: {{item.links.replies[0].count}}</a>
               </h1>
               {{item.object.content | html}}
               <div ng:repeat="reply in item.replies.data.items" style="margin-left: 20px;">
                 <img src="{{reply.actor.thumbnailUrl}}" style="max-height:30px;max-width:30px;"/>
                 <a href="{{reply.actor.profileUrl}}">{{reply.actor.name}}</a>: {{reply.content | html}}
               </div>
             </div>
           </div>