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Response Formatting
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===================
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When handling a RESTful API request, an application usually takes the following steps that are related
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with response formatting:
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1. Determine various factors that may affect the response format, such as media type, language, version, etc.
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This process is also known as [content negotiation](http://en.wikipedia.org/wiki/Content_negotiation).
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2. Convert resource objects into arrays, as described in the [Resources](rest-resources.md) section.
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This is done by [[yii\rest\Serializer]].
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3. Convert arrays into a string in the format as determined by the content negotiation step. This is
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done by [[yii\web\ResponseFormatterInterface|response formatters]] registered with
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the [[yii\web\Response::formatters|formatters]] property of the
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`response` [application component](structure-application-components.md).
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## Content Negotiation <span id="content-negotiation"></span>
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Yii supports content negotiation via the [[yii\filters\ContentNegotiator]] filter. The RESTful API base
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controller class [[yii\rest\Controller]] is equipped with this filter under the name of `contentNegotiator`.
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The filter provides response format negotiation as well as language negotiation. For example, if a RESTful
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API request contains the following header,
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```
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Accept: application/json; q=1.0, */*; q=0.1
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```
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it will get a response in JSON format, like the following:
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```
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$ curl -i -H "Accept: application/json; q=1.0, */*; q=0.1" "http://localhost/users"
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HTTP/1.1 200 OK
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Date: Sun, 02 Mar 2014 05:31:43 GMT
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Server: Apache/2.2.26 (Unix) DAV/2 PHP/5.4.20 mod_ssl/2.2.26 OpenSSL/0.9.8y
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X-Powered-By: PHP/5.4.20
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X-Pagination-Total-Count: 1000
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X-Pagination-Page-Count: 50
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X-Pagination-Current-Page: 1
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X-Pagination-Per-Page: 20
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Link: <http://localhost/users?page=1>; rel=self,
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<http://localhost/users?page=2>; rel=next,
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<http://localhost/users?page=50>; rel=last
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Transfer-Encoding: chunked
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Content-Type: application/json; charset=UTF-8
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[
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{
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"id": 1,
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...
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},
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{
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"id": 2,
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...
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},
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...
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]
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```
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Behind the scene, before a RESTful API controller action is executed, the [[yii\filters\ContentNegotiator]]
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filter will check the `Accept` HTTP header in the request and set the [[yii\web\Response::format|response format]]
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to be `'json'`. After the action is executed and returns the resulting resource object or collection,
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[[yii\rest\Serializer]] will convert the result into an array. And finally, [[yii\web\JsonResponseFormatter]]
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will serialize the array into a JSON string and include it in the response body.
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By default, RESTful APIs support both JSON and XML formats. To support a new format, you should configure
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the [[yii\filters\ContentNegotiator::formats|formats]] property of the `contentNegotiator` filter like
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the following in your API controller classes:
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```php
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use yii\web\Response;
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public function behaviors()
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{
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$behaviors = parent::behaviors();
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$behaviors['contentNegotiator']['formats']['text/html'] = Response::FORMAT_HTML;
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return $behaviors;
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}
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```
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The keys of the `formats` property are the supported MIME types, while the values are the corresponding
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response format names which must be supported in [[yii\web\Response::formatters]].
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## Data Serializing <span id="data-serializing"></span>
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As we have described above, [[yii\rest\Serializer]] is the central piece responsible for converting resource
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objects or collections into arrays. It recognizes objects implementing [[yii\base\ArrayableInterface]] as
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well as [[yii\data\DataProviderInterface]]. The former is mainly implemented by resource objects, while
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the latter resource collections.
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You may configure the serializer by setting the [[yii\rest\Controller::serializer]] property with a configuration array.
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For example, sometimes you may want to help simplify the client development work by including pagination information
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directly in the response body. To do so, configure the [[yii\rest\Serializer::collectionEnvelope]] property
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as follows:
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```php
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use yii\rest\ActiveController;
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class UserController extends ActiveController
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{
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public $modelClass = 'app\models\User';
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public $serializer = [
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'class' => 'yii\rest\Serializer',
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'collectionEnvelope' => 'items',
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];
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}
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```
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You may then get the following response for request `http://localhost/users`:
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```
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HTTP/1.1 200 OK
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Date: Sun, 02 Mar 2014 05:31:43 GMT
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Server: Apache/2.2.26 (Unix) DAV/2 PHP/5.4.20 mod_ssl/2.2.26 OpenSSL/0.9.8y
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X-Powered-By: PHP/5.4.20
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X-Pagination-Total-Count: 1000
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X-Pagination-Page-Count: 50
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X-Pagination-Current-Page: 1
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X-Pagination-Per-Page: 20
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Link: <http://localhost/users?page=1>; rel=self,
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<http://localhost/users?page=2>; rel=next,
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<http://localhost/users?page=50>; rel=last
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Transfer-Encoding: chunked
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Content-Type: application/json; charset=UTF-8
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{
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"items": [
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{
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"id": 1,
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...
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},
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{
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"id": 2,
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...
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},
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...
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],
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"_links": {
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"self": {
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"href": "http://localhost/users?page=1"
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},
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"next": {
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"href": "http://localhost/users?page=2"
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},
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"last": {
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"href": "http://localhost/users?page=50"
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}
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},
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"_meta": {
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"totalCount": 1000,
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"pageCount": 50,
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"currentPage": 1,
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"perPage": 20
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}
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}
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```
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