I don't want to create a discussion about singleton better than static or better than global, etc. I read dozens of questions about it on SO, but I couldn't come up with an answer to this SPECIFIC question, so I hope someone could now illuminate me buy answering this question with one (or more) real simple EXAMPLES, and not theoretical discussions.
In my app I have the typical DB class needed to perform tasks on DB without having to write everywhere in code mysql_connect/mysql_select_db/mysql... (moreover in future I might decide to use another type of DB engine in place of mySQL so obviously I need a class of abstration).
I could write the class either as a static class:
class DB
{
private static $connection = FALSE; //connection to be opened
//DB connection values
private static $server = NULL; private static $usr = NULL; private static $psw = NULL; private static $name = NULL;
public static function init($db_server, $db_usr, $db_psw, $db_name)
{
//simply stores connections values, withour opening connection
}
public static function query($query_string)
{
//performs query over alerady opened connection, if not open, it opens connection 1st
}
...
}
or as a Singletonm class:
class DBSingleton
{
private $inst = NULL;
private $connection = FALSE; //connection to be opened
//DB connection values
private $server = NULL; private $usr = NULL; private $psw = NULL; private $name = NULL;
public static function getInstance($db_server, $db_usr, $db_psw, $db_name)
{
//simply stores connections values, withour opening connection
if($inst === NULL)
$this->inst = new DBSingleton();
return $this->inst;
}
private __construct()...
public function query($query_string)
{
//performs query over already opened connection, if connection is not open, it opens connection 1st
}
...
}
Then after in my app if I wanto to query the DB i could do
//Performing query using static DB object
DB:init(HOST, USR, PSW, DB_NAME);
DB::query("SELECT...");
//Performing query using DB singleton
$temp = DBSingleton::getInstance(HOST, USR, PSW, DB_NAME);
$temp->query("SELECT...");
My simple brain sees Singleton has got the only advantage to avoid declaring as 'static' each method of the class. I'm sure some of you could give me an EXAMPLE of real advantage of singleton in this specific case. Thanks in advance.
