Question

I am trying to write a db util class using the singleton pattern. My problem is that the “connection” object is always null. The connection settings are correct. What could i be doing wrong ? Also, i am relatively new to php development. What method should i use to figure out what’s wrong ? Code follows.

   class DBUtil {
        public $connection = NULL; //mysqli_connection object
        private static $instance = NULL;

        private function _constructor($conn){
            //$this->connection = mysqli_connect(TagMetroConfiguration::getConfigurationValueFor("db_servser_name"), TagMetroConfiguration::getConfigurationValueFor("db_username"), TagMetroConfiguration::getConfigurationValueFor("db_password"), TagMetroConfiguration::getConfigurationValueFor("db_name"));
            $this->connection = new mysqli("localhost", "root", "toor", "testdb");
        }

        public static function getInstance(){
            if(DBUtil::$instance == NULL){
                try{
                    DBUtil::$instance = new DBUtil();
                }catch(Exception $ex){
                    throw new Exception("Unable to create DB Instance");
                }
            }

            return DBUtil::$instance;
        }
}

Answer 1

Your constructor function should be named __construct (notice two underscores).

Also, in your constructor, you have one parameter, $conn. When you call new DBUtil(), you are not providing that input parameter, so perhaps it’s calling the default contructor, not your custom one.

If you want the input parameter $conn to be optional, try __construct($conn = null).

Or try calling it as new DBUtil(null).