Exceptions are a core PHP feature, but they are seldom used fairly. Yii makes exceptions very useful.
There are two main areas where Yii exceptions come in handy, which are as follows:
Generally, an exception should be thrown when a component cannot handle a special situation, such as the one said earlier, and needs to leave it to higher-level components.
Let's assume that we have an
application/apis/lyrics/LyricsFinder.phpclass that makes an HTTP request to an API using CURL and returns song lyrics based on its name. This is how we can use exceptions inside of it:// create some custom exceptions to be able to catch them // specifically if needed // general lyrics finder exception class LyricsFinderException extends CException {} // used when there is a connection problem class LyricsFinderHTTPException extends LyricsFinderException{} class LyricsFinder { private $apiUrl = 'http://example.com/lyricsapi&songtitle=%s'; function getText($songTitle) { $url = $this->getUrl($songTitle); $curl = curl_init(); curl_setopt($curl, CURLOPT_URL, $url); curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1); $result = curl_exec($curl); // if there is an HTTP error, we'll throw an exception if($result===false) { $errorText = curl_error($curl); curl_close($url); throw new LyricsFinderHTTPException($errorText); } curl_close($curl); return $result; } private function getRequestUrl($songTitle) { return sprintf($this->apiUrl, urlencode($songTitle)); } }As we don't know how a specific application needs to handle its API connection, we will leave it to the application itself by throwing a custom
LyricsFinderHTTPException. This is how we can handle it in ourprotected/controllers/TestController.php:class TestController extends CController { public function actionIndex($song) { $lyric = 'Nothing was found.'; // importing api class Yii::import('application.apis.lyrics.LyricsFinder'); $finder = new LyricsFinder(); if(!empty($song)) { // We don't want to show user an error. // Instead we want to apologize and // invite him to try again later. try { $lyric = $finder->getText($song); } // we are looking for specific exception here catch (LyricsFinderHTTPException $e) { echo 'Sorry, we cannot process your request. Try again later.'; } } echo $lyric; } }Another usage of Yii exceptions is the generation of different HTTP responses by throwing
CHttpException. For example, an action that displays a blog post represented by aPostmodel, loaded by its ID will look like this:class PostController extends CController { function actionView() { if(!isset($_GET['id'])) // If there is no post ID supplied, request is definitely wrong. // According to HTTP specification its code is 400. throw new ChttpException(400); // Finding a post by its ID $post = Post::model()->findByPk($_GET['id']); if(!$post) // If there is no post with ID specified we'll generate // HTTP response with code 404 Not Found. throw new CHttpException(404); // If everything is OK, render a post $this->render('post', array('model' => $post)); } }
Yii converts all non-fatal application errors to CException automatically.
Additionally, the default exception handler raises either the onError or an onException event. The default event handler writes a log message with error level set to error. Additionally, if your application's YII_DEBUG constant is set to true, unhandled exception or error will be displayed at a handy error screen. This screen includes a call stack trace, a code area where the exception was raised, and the file and line where you can look for the code to fix.
For further information, refer to the following URLs: