【Yii】CDataProvider

CDataProvider，顾名思义，数据提供者，它提供了三个抽象方法(fetchData,、fetchKeys 和 calculateTotalItemCount)，分别为调用不同数据结构的数据提供了获取数据、获取键值、获取数量的，接口，在YII框架中，CActiveDataProvider、CArrayDataProvider、CSqlDataProvider是它的子类，除了提供数据之外，他还提供分页和排序功能。下面以获取数据fetchData()为例

CActiveDataProvider通过CActiveRecord的子类和CDbCriteria对象

 /**
     * Fetches the data from the persistent data storage.
     * @return array list of data items
     */
 protected function fetchData()
 {
     $criteria=clone $this->getCriteria();

     if(($pagination=$this->getPagination())!==false)
     {
         $pagination->setItemCount($this->getTotalItemCount());
         $pagination->applyLimit($criteria);
     }

     $baseCriteria=$this->model->getDbCriteria(false);

     if(($sort=$this->getSort())!==false)
     {
         // set model criteria so that CSort can use its table alias setting
         if($baseCriteria!==null)
         {
             $c=clone $baseCriteria;
             $c->mergeWith($criteria);
             $this->model->setDbCriteria($c);
         }
         else
             $this->model->setDbCriteria($criteria);
         $sort->applyOrder($criteria);
     }

     $this->model->setDbCriteria($baseCriteria!==null ? clone $baseCriteria : null);
     $data=$this->model->findAll($criteria);

     $this->model->setDbCriteria($baseCriteria);  // restore original criteria
     return $data;
 }

CArrayDataProvider通过传人的原生数据来获取数据

 /**
     * Fetches the data from the persistent data storage.
     * @return array list of data items
     */
 protected function fetchData()
 {
     if(($sort=$this->getSort())!==false && ($order=$sort->getOrderBy())!='')
         $this->sortData($this->getSortDirections($order));

     if(($pagination=$this->getPagination())!==false)
     {
         $pagination->setItemCount($this->getTotalItemCount());
         return array_slice($this->rawData, $pagination->getOffset(), $pagination->getLimit());
     }
     else
         return $this->rawData;
 }

CSqlDataProvider通过传人的sql，经过db执行获取数据

 /**
     * Fetches the data from the persistent data storage.
     * @return array list of data items
     */
 protected function fetchData()
 {
     $sql=$this->sql;
     $db=$this->db===null ? Yii::app()->db : $this->db;
     $db->active=true;

     if(($sort=$this->getSort())!==false)
     {
         $order=$sort->getOrderBy();
         if(!empty($order))
         {
             if(preg_match('/\s+order\s+by\s+[\w\s,]+$/i',$sql))
                 $sql.=', '.$order;
             else
                 $sql.=' ORDER BY '.$order;
         }
     }

     if(($pagination=$this->getPagination())!==false)
     {
         $pagination->setItemCount($this->getTotalItemCount());
         $limit=$pagination->getLimit();
         $offset=$pagination->getOffset();
         $sql=$db->getCommandBuilder()->applyLimit($sql,$limit,$offset);
     }

     $command=$db->createCommand($sql);
     foreach($this->params as $name=>$value)
         $command->bindValue($name,$value);

     return $command->queryAll();
 }