数据访问对象模式

// 这是一个单利模式用于提供mysql pdo链接
class MysqlConnect
{
    protected $link = null;
    protected static $instance = null;

    public static function getInstance()
    {
        if (is_null(self::$instance)) {
            self::$instance = new MysqlConnect();
        }
        return self::$instance;
    }

    protected function __construct()
    {
        $this->connect();
    }

    public function connect()
    {
        if (is_null($this->link)) {
            $this->link = new PDO(‘mysql:host=127.0.0.1;dbname=test‘, ‘root‘, ‘root‘);
        }
    }

    public function close()
    {
        $this->link = null;
    }

    public function getLink()
    {
        return $this->link;
    }
}

abstract class DAO
{

    protected $table = null;
    protected $link = null;

    public function __construct()
    {
        $this->link = MysqlConnect::getInstance()->getLink();
    }



    public function fetch()
    {
        $res = $this->link->query("SELECT * FROM {$this->table}");
        $data = array();

        foreach ($res as $row) {
            $data[] = $row;
        }
        return $data;
    }
}

class CD extends DAO
{
    protected $table = ‘cd‘;
}

$cd = new CD();
var_dump($cd->fetch());