A php pdo mysql operation class

/**
 * PDO 操作
 * Created by PhpStorm.
 * User: sumiaowen
 * Date: 13-11-28
 * Time: 下午9:12
 * To change this template use File | Settings | File Templates.
*/
class Pdo_db
{
 private $dns = null;
 private $username = null;
 private $password = null;
 private $conn = null;
 private static $_instance = null;
 private function __construct($params = array())
 {
  $this->dns      = $params['dns'];
  $this->username = $params['username'];
  $this->password = $params['password'];
  $this->_connect();
 }
 private function __clone() { }
 public function get_instance($params = array())
 {
  if(!(self::$_instance instanceof self))
  {
   self::$_instance = new self($params);
  }
  return self::$_instance;
 }
 private function _connect()
 {
  try
  {
   $this->conn = new PDO($this->dns, $this->username, $this->password);
   $this->conn->query('set names utf8');
  }
  catch(PDOException $e)
  {
   exit('PDOException: ' . $e->getMessage());
  }
 }
 /**
 * Query a SQL statement
 * @param string $sql
 * @param array $parameters Parameters that need to be bound
 * @param int $option
 * @return array
*/
 public function query($sql, $parameters = array(), $option = PDO::FETCH_ASSOC)
 {
  $stmt = $this->conn->prepare($sql);
  $stmt->execute($parameters);
  $tmp = array();
  while($row = $stmt->fetch($option))
  {
   $tmp[] = $row;
  }
  return $tmp;
 }
 /**
 * Insert a piece of data
 * @param string $sql
 * @param array $parameters
 * @return int 1 or 0 Return the number of affected rows
*/
 public function insert($sql, $parameters = array())
 {
  $stmt = $this->conn->prepare($sql);
  $stmt->execute($parameters);
  return $stmt->rowCount();
 }
 /**
 * Update a piece of data
 * @param string $sql
 * @param array $parameters
 * @return int 1 or 0 Return the number of affected rows
*/ bbs.it-home.org
 public function update($sql, $parameters = array())
 {
  $stmt = $this->conn->prepare($sql);
  $stmt->execute($parameters);
  return $stmt->rowCount();
 }
 /**
 * Delete a piece of data
 * @param string $sql
 * @param array $parameters
 * @return int 1 or 0 Return the number of affected rows
*/
 public function delete($sql, $parameters = array())
 {
  $stmt = $this->conn->prepare($sql);
  $stmt->execute($parameters);
  return $stmt->rowCount();
 }
}

代码链接地址：https://github.com/sumiaowen/mynotes/tree/master/pdo_mysql_class