Establishing database connection in php using singleton class - php

Question

Can anybody please guide me with a sample code to establish a database connection in php using singleton class.

Answer 1

class DatabaseSingleton
{
// [Singleton]
private static $instance = null;
public static function getInstance()
{
if (!self::$instance)
{
self::$instance = new self();
}
return self::$instance;
}
private function __clone(){}
// [/Singleton]
private $connection = null;
private function __construct()
{
$this->connection = mysql_connect('localhost','root','admin');
if ($this->connection)
{
mysql_select_db('my_database');
}
}
//
// crud operations go here.
//
}
$db = DatabaseSingleton::getInstance();
$db->SomeCRUDOperation();
Something like that perhaps? Very basic, but should give you a starting point.

Answer 2

That's how a singleton-pattern looks like:
<?php
class SingletonClass
{
static private $instance = null;
static public function getInstance()
{
if (null === self::$instance) {
self::$instance = new self;
}
return self::$instance;
}
private function __construct(){}
private function __clone(){}
}
$singletonClass = SingletonClass::getInstance();
Now you can put random functions and parameters in there that handle your DB-stuff. I hope that answers your question.

Answer 3

See the manual for an example on how to implement the Singleton pattern: http://www.php.net/manual/en/language.oop5.patterns.php
Then just establish the database connection in your class constructor.

Answer 4

I use something like this:
class DBConn
{
static private $_db = null; // The same PDO will persist from one call to the next
private function __construct() {} // disallow calling the class via new DBConn
private function __clone() {} // disallow cloning the class
/**
* Establishes a PDO connection if one doesn't exist,
* or simply returns the already existing connection.
* #return PDO A working PDO connection
*/
static public function getConnection()
{
if (self::$_db == null) { // No PDO exists yet, so make one and send it back.
try {
self::$_db = new PDO('mysql:host=' . DB_HOST . ';dbname=' . DB_NAME, DB_USER, DB_PASS);
} catch (PDOException $e) {
// Use next line for debugging only, remove or comment out before going live.
// echo 'PDO says: ' . $e->getMessage() . '<br />';
// This is all the end user should see if the connection fails.
die('<h1>Sorry. The Database connection is temporarily unavailable.</h1>');
} // end PDO connection try/catch
return self::$_db;
} else { // There is already a PDO, so just send it back.
return self::$_db;
} // end PDO exists if/else
} // end function getConnection
} // end class DBConn
/**
* And you can use it as such in a class
* */
class Post {
public function __construct(){
$this->db = DBConn::getConnection();
}
public function getPosts()
{
try {
/*** The SQL SELECT statement ***/
$sql = "SELECT * FROM posts";
foreach ($this->_dbh->query($sql) as $row) {
var_dump($row);
}
/*** close the database connection ***/
$this->_dbh = null;
} catch (PDOException $e) {
echo $e->getMessage();
}
}
}

Answer 5

I am using something like below
class Database
{
private $_connection;
private static $_instance; //The single instance
private $_host = "HOST";
private $_username = "USERNAME";
private $_password = "PASSWORd";
private $_database = "DATABASE";
public static function getInstance() {
if(!self::$_instance) { // If no instance then make one
self::$_instance = new self();
}
return self::$_instance;
}
private function __construct() {
$this->_connection = new mysqli($this->_host, $this->_username,
$this->_password, $this->_database);
// Error handling
if(mysqli_connect_error()) {
trigger_error("Failed to conencto to MySQL: " . mysqli_connect_error(),
E_USER_ERROR);
}
}
// Magic method clone is for prevent duplication of connection
private function __clone() { }
public function getConnection() {
return $this->_connection;
}
}
$db = Database::getInstance();
$mysqli = $db->getConnection();
$sql_query = "SELECT foo FROM etc";
$result = $mysqli->query($sql_query);