数据缓存中的依赖关系

1、缓存文件依赖

 $cache = \YII::$app->cache;
        $dependency = new \yii\caching\FileDependency(['fileName'=>'hw.txt']);
        $cache->add('file_key','hello world',3000,$dependency);
        var_dump($cache->get('file_key'));

当hw.txt文件中的内容出现变化，则该缓存过期

2、表达式依赖：

$cache = \YII::$app->cache;
        $dependency = new \yii\caching\ExpressionDependency(['expression'=>'\YII::$app->request->get("name")']);
        $cache->add('expression_key','hello world',3000,$dependency);
        var_dump($cache->get('expression_key'));

当 ['expression'=>'\YII::$app->request->get("name")'] 中获得的name的值发生了变化，则缓存过期

3、DB依赖

$cache=\YII::$app->cache;
        $dependency = new \yii\caching\DbDependency(
            ['sql'=>'SELECT count(*) FROM yii.order']
        );
        $cache->add('db_key','hello_world',3000,$dependency);
        var_dump($cache->get('db_key'));