Hvordan bruger man Persistent Connection of PDO?

Dette spørgsmål er meget gammelt, men det vil være okay, hvis jeg bidrager. Jeg tror, ​​du skal implementere en singleton-klasse til at håndtere databaseforbindelser, jeg vil skrive en prøveklasse nedenfor ..

<?php
class DB{

//set the connection property to private to prevent direct access 
private static $conn;

//now since we dont want to reinstiate the class anytime we need it, lets also set the constructor to private 
private function __construct(){}

//now lets create our method for connecting to the database 
public static function connect(){

//now lets check if a connection exists already in our $conn property, then we should return it instead of recreating a new connection 
if(!empty(self::$conn)){
return self::$conn;
}//end if 

//upon reaching here means the $conn property is empty so lets create a new connection 

try {
 $dbh = new PDO('mysql:host=127.0.0.1;dbname=lingtong', 'root', 'xxxxxx', array(PDO::ATTR_PERSISTENT => true));

//lets now assign the database connection to our $conn property 
self::$conn = $dbh;

//return the connection 
return $dbh;

} catch (PDOException $e) {
 print "Error! : " . $e->getMessage() . "<br/>";
 die();
}

}//end method 

}//end class

?>

Vores singleton-klasse kan kun oprette én forbindelse og genbruge den, lad os se, hvordan vi kan bruge vores klasse

<?php 
$dbh = DB::connect();

foreach ($dbh->query('SELECT * from agent') as $row){ 
  print_r($row);
}
?>