libs/Yii/web/widgets/COutputCache.php

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<?php
/**
 * COutputCache class file.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @link http://www.yiiframework.com/
 * @copyright Copyright &copy; 2008-2011 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

/**
 * COutputCache enables caching the output generated by an action or a view fragment.
 *
 * If the output to be displayed is found valid in cache, the cached
 * version will be displayed instead, which saves the time for generating
 * the original output.
 *
 * Since COutputCache extends from {@link CFilterWidget}, it can be used
 * as either a filter (for action caching) or a widget (for fragment caching).
 * For the latter, the shortcuts {@link CBaseController::beginCache()} and {@link CBaseController::endCache()}
 * are often used instead, like the following in a view file:
 * <pre>
 * if($this->beginCache('cacheName',array('property1'=>'value1',...))
 * {
 *     // ... display the content to be cached here
 *    $this->endCache();
 * }
 * </pre>
 *
 * COutputCache must work with a cache application component specified via {@link cacheID}.
 * If the cache application component is not available, COutputCache will be disabled.
 *
 * The validity of the cached content is determined based on two factors:
 * the {@link duration} and the cache {@link dependency}.
 * The former specifies the number of seconds that the data can remain
 * valid in cache (defaults to 60s), while the latter specifies conditions
 * that the cached data depends on. If a dependency changes,
 * (e.g. relevant data in DB are updated), the cached data will be invalidated.
 * For more details about cache dependency, see {@link CCacheDependency}.
 *
 * Sometimes, it is necessary to turn off output caching only for certain request types.
 * For example, we only want to cache a form when it is initially requested;
 * any subsequent display of the form should not be cached because it contains user input.
 * We can set {@link requestTypes} to be <code>array('GET')</code> to accomplish this task.
 *
 * The content fetched from cache may be variated with respect to
 * some parameters. COutputCache supports four kinds of variations:
 * <ul>
 * <li>{@link varyByRoute}: this specifies whether the cached content
 *   should be varied with the requested route (controller and action)</li>
 * <li>{@link varyByParam}: this specifies a list of GET parameter names
 *   and uses the corresponding values to determine the version of the cached content.</li>
 * <li>{@link varyBySession}: this specifies whether the cached content
 *   should be varied with the user session.</li>
 * <li>{@link varyByExpression}: this specifies whether the cached content
 *   should be varied with the result of the specified PHP expression.</li>
 * </ul>
 * For more advanced variation, override {@link getBaseCacheKey()} method.
 *
 * @property boolean $isContentCached Whether the content can be found from cache.