PHP設計模式-DAO (Data Access Objects) 數據訪問對象模式

整理一下本身的學習Aaron Saray 寫的PHP設計模式一些demo和本身的理解。大佬看完若是發現鄙人理解有誤請當即指出，感謝拍磚，跪求鞭打

/**
 * DAO (Data Access Objects) 數據訪問對象
 * -------------------------------------
 * ** 來自說明 **
 *
 * 數據訪問對象設計模式描述瞭如何建立提供透明訪問任何數據源的對象
 *
 * 目的是解決下列兩種特定的問題：
 *     1. 重複
 *  2. 數據源抽象化
 *  數據訪問對象模式提供數據庫抽象層
 *  如今，應用程序的主要處理代碼再也不考慮數據庫引擎或表關係
 *  調用這種對象的公共方法會返回任何數據類型，不用考慮內在SQL所需的類型
 * 
 * ===================================== 
 * ** 應用場景 **
 *
 * 數據訪問
 * 
 * -------------------------------------
 * 
 * @version ${Id}$
 * @author Shaowei Pu <54268491@qq.com>
 */

abstract class baseDao{
    /**
     * [$_connection 鏈接對象]
     * @var [type]
     */
    private $_connection;

    /**
     * [__construct 實例化數據庫鏈接]
     * @author         Shaowei Pu <pushaowei@sporte.cn>
     * @CreateTime    2017-02-22T17:52:04+0800
     */
    public function __construct(){
        try{        
            $this->_connection = new \PDO("mysql:dbname=mysql;host=localhost","root","pushaowei");
            $this->_connection->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);
        }catch(PDOException $e){
            die('error:'.$e->getMessage());
        }   
    }
    /**
     * [feach description]
     * @author         Shaowei Pu <pushaowei@sporte.cn>
     * @CreateTime    2017-02-22T18:01:48+0800
     * @return                              [type] [description]
     */
    public function fetch( $value , $key = ''){
        // SQL START
        $sql = 'SELECT * FROM '.$this->_tablename.' WHERE '.$key.' = "'.$value.'"';
        // 輸出
        $dispose = $this->_connection->query($sql);
        return $dispose->fetch(PDO::FETCH_ASSOC);        
    }

}
class selectHandle extends baseDao{
    /**
     * [$_tablename 獲得表名]
     * @var string
     */
    protected $_tablename = 'db';

    /**
     * [getValue description]
     * @author         Shaowei Pu <pushaowei@sporte.cn>
     * @CreateTime    2017-02-22T18:06:58+0800
     * @param                               [type] $value [description]
     * @return                              [type]        [description]
     */
    public function getDbValue( $value ){
        $result = parent::fetch( $value, 'Host' );
        return $result;
    }
}

$select = new selectHandle;
var_dump($select->getDbValue('localhost'));

/* 
+----------------------------------------------------------------------
|    array (size=22)
|      'Host' => string 'localhost' (length=9)
|      'Db' => string 'sys' (length=3)
|      'User' => string 'mysql.sys' (length=9)
|      'Select_priv' => string 'N' (length=1)
|      'Insert_priv' => string 'N' (length=1)
|      'Update_priv' => string 'N' (length=1)
|      'Delete_priv' => string 'N' (length=1)
|      'Create_priv' => string 'N' (length=1)
|      'Drop_priv' => string 'N' (length=1)
|      'Grant_priv' => string 'N' (length=1)
|      'References_priv' => string 'N' (length=1)
|      'Index_priv' => string 'N' (length=1)
|      'Alter_priv' => string 'N' (length=1)
|      'Create_tmp_table_priv' => string 'N' (length=1)
|      'Lock_tables_priv' => string 'N' (length=1)
|      'Create_view_priv' => string 'N' (length=1)
|      'Show_view_priv' => string 'N' (length=1)
|      'Create_routine_priv' => string 'N' (length=1)
|      'Alter_routine_priv' => string 'N' (length=1)
|      'Execute_priv' => string 'N' (length=1)
|      'Event_priv' => string 'N' (length=1)
|      'Trigger_priv' => string 'Y' (length=1)
+----------------------------------------------------------------------
*/