使用MVC类进行两次PDO连接

Question

I'm new in MVC, I try to put PDO into my model

I extends PDO in my Model & page model extends from Model

PDO->Model->Page Model

my problem is because page model extends Model, so it will construct connect db again. (Model has to construct connect db, because it extends from PDO)

anyone know how to fix this?

class Model extends PDO{

    protected   $dsn        = "mysql:host=127.0.0.1; dbname=abc; charset=utf8;",
                $username   = "member", 
                $password   = "123",
                $options    = array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8');

    public function __construct(){
        //connect db
        parent::__construct($this->dsn, $this->username, $this->password, $this->options);
        echo "db connect";
    }
}

class index_model extends Model{

    public function __construct(){
        parent::__construct();
        //if i don't add this, will get error,
        //but if i add, I will connect db twice   
    }

    public function mainData(){
        $sql = parent::prepare("SELECT pday FROM pday");    
        $sql->execute();
        $data = $sql->fetch(PDO::FETCH_ASSOC);
        echo $data['pday'];
    }
}

Answer 1

I have fix my problem, I create another class for connection,

and put this inside of Model method, page model extends model, so it will not construct connection twice.

class Model{
   protected $db;

   public function connect(){
            $this->db = new DB;
   }
}

class DB extends PDO{
    protected   $dsn        = "mysql:host=127.0.0.1; dbname=abc; charset=utf8;",
                $username   = "member", 
                $password   = "123",
                $options    = array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8');

    public function __construct(){
          parent::__construct($this->dsn, $this->username, $this->password, $this->options);
    }
}

class index_model extends Model{
    private $sql;

    public function mainData(){
        $this->sql = $this->db->prepare("...");
        ...
    }
}

$index = new index_model;
$index->connect();
$index->mainData();