mysqli constructor returns null

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;
        }
}

Well actually, the singleton pattern looks too complicated to you, but that's not a problem at all: Just don't use singletons. You don't need them in PHP. In your case you only need a global variable for the database connection. - But if you feel like copy and paste, [the PHP manual has a code example for the Singleton Pattern](http://php.net/manual/en/language.oop5.patterns.php#language.oop5.patterns.singleton) (not that this makes anything better, don't use it ). [Who needs singletons?](http://stackoverflow.com/q/4595964/367456). — hakre, Apr 11 '12 at 14:27

Travesty3 · Accepted Answer · 2012-04-11T14:30:42.747

3

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).

edited Apr 11 '12 at 14:30

answered Apr 11 '12 at 14:24

Travesty3

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score 2 · Answer 2 · answered Apr 11 '12 at 14:25

2

private function _constructor($conn)   ??

should this be

private function __construct($conn)

answered Apr 11 '12 at 14:25

Lee Davis

4,685
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Also might want to set the default value to null, as your not passing a $conn variable when instantiating the object. private function __construct($conn = null) – Lee Davis Apr 11 '12 at 14:30

score 2 · Answer 3 · edited Apr 17 '12 at 22:19

2

There should be two underscores __ (__construct).

edited Apr 17 '12 at 22:19

answered Apr 11 '12 at 14:38

Sudantha

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score -1 · Answer 4 · answered Apr 11 '12 at 14:28

You should do like this :

class DBUtil {

        private static $instance;

        private function _construct(){
            $this->$instance = new mysqli("localhost", "root", "toor", "testdb");
        }

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

            return self::$instance;
        }

mysqli constructor returns null

4 Answers4