YII缓存操作

//文件依赖

$dependency = new \yii\caching\FileDependency(['filename'=>'hw.txt'])};

$cache->add("file_key",'hello world',3000,$dependency);//$dependency决定了当缓存文件发生修改时也会失效

//表达式的依赖

$dependency = new \yii\caching\ExpressionDependency(
['expression'=>'\Yii::$app->request->get("name")']
);
$cache->add("expression_key","hello world",3000,$dependency);
//当name的值发生变化时也会失效

//DB依赖
$dependency = new \yii\caching\DbDependency(
    ['sql'=>'SELECT COUNT(*) FROM yii.order']
);
$cache->add('db_key','hello world',$dependency);
//当sql查询出来的结果发生变化时也会失效

$cache->flush()//清掉所有缓存

$cache->add();//会判断当前键cache是否存在，如果存在就不会添加