define('DB','sistema_postgres');
define('HOST','localhost');
define('USER','postgres');
define('PASS','123');

require_once 'config.php';
class Database {
   private $db;
   private $host;
   private $user;
   private $pass;
   private $conn;

   public function __construct(){
     $this->host = HOST;
     $this->db = DB;
     $this->user = USER;
     $this->pass = PASS;
     $this->conn = new PDO("pgsql:host={$this->host};port=5432;dbname={$this->db};user={$this->user};password={$this->pass}");
   }

   protected function getConn(){
     return $this->conn;
   }
}

require_once('database.php');
class TurmaDAO extends Database implements IDAO{
    private $turma;
    private $db;

    public function __construct($turma=null) {
        if(isset($turma)){
            $this->setTurma($turma);
        }
        parent::__construct();
        $this->db = parent::getConn();
    }

    public function listAll() {
        $stmt = $this->db->prepare('SELECT * FROM turma');
        $stmt->execute();
        try{
            $rs = $stmt->fetchAll(PDO::FETCH_ASSOC);
        }
        catch(PDOException $e){
            echo $e->getMessage();
            die();
        }
        return $rs;
    }
}

require_once 'TurmaDAO.php';
$t = new TurmaDAO();
$rs = $t->listAll();
var_dump($rs);