php - Yii CActiveDataProvider 查询缓存无法正常工作

Question

我想缓存 CActiveDataProvider 实例的数据库结果。

我在 Controller 的操作中准备数据提供者，然后在 CGridView 中使用数据提供者，稍后在某些 View 中使用。

我曾经有过这样的代码:

$cars=new CActiveDataProvider(
    'Car'
    ,
    array(
        'criteria'=>array(
            'condition'=>'brand_id=:brand_id',
            'params' => array(':brand_id'=>$model->id),
            'order' => 'price',
        ),
        'pagination'=>false,
    )
);

然后，在 tutorial in the yii wiki 之后，我改成了:

$cars=new CActiveDataProvider(
        Car::model()->cache(3600)
        ,
        array(
            'criteria'=>array(
                'condition'=>'brand_id=:brand_id',
                'params' => array(':brand_id'=>$model->id),
                'order' => 'price',
            ),
            'pagination'=>false,
        )
    );

但无济于事:查询未被缓存。

Answer 1

CActiveDataProvider 的优点之一是查询不会立即执行。只有当您稍后使用 CActiveDataProvider 时才会执行查询，比如在 CGridView 中，它将调用 CActiveDataProvider::fetchData最终触发查询。

这很有用，因为您可以使用片段缓存，并且您不希望在 Controller 中加载数据只是为了发现您不需要它，因为片段已被缓存。

这正是这里发生的事情:ActiveRecord ->cache() method指示 DB Connection 缓存后续查询，但如果查询没有立即执行，则可能在此查询之前执行其他查询，并且此缓存将不起作用。

我解决了创建个性化 ActiveDataProvider 的问题，它将在查询发生之前设置模型缓存:

class CachedActiveDataProvider extends CActiveDataProvider
{

    public $cache_duration = null;
    public $cache_dependency = null;

    /**
     * The cache mechanism works by telling the DB Component to cache the next query.
     * When  fetchData() is called, the DB will cache the next query. 
     * There is a possibility that fetchData call calculateTotalItemCount()
     * and in that function, if this bit is active, we will tell the DB to cache
     * 2 queries, the count, and the actual fetch that will come next.
     * (if we don't do this, the DB will cache the count query, and will forget about
     * the instruction to cache the fetch query)
     * 
     * @var boolean
     */
    private $fetching_data = false;

    protected function fetchData()
    {
        if (!is_null($this->cache_duration ))
        {
            $this->model->cache($this->cache_duration, $this->cache_dependency);
        }

        $this->fetching_data = true;
        $ret = parent::fetchData();
        $this->fetching_data = false;

        return $ret;
    }

    protected function calculateTotalItemCount()
    {
        if (!is_null($this->cache_duration ))
        {
            $this->model->cache(
                $this->cache_duration, 
                $this->cache_dependency, 
                $this->fetching_data ? 2 : 1 //if fetching data, cache 2 queries: this count and the sequent fetching
            );
        }

        return parent::calculateTotalItemCount();
    }
}

我现在可以调用它了

$cars=new CachedActiveDataProvider(
    'Car'
    ,
    array(
        'criteria'=>array(
            'condition'=>'brand_id=:brand_id',
            'params' => array(':brand_id'=>$model->id),
            'order' => 'price',
        ),
        'pagination'=>false,
        'cache_duration' => 3600,
    )
);