 PHP Page 3 - Building a Singleton Database with Restrictive Constructors in PHP 5 |
Adding methods: fetching rows, finding insertion IDs and more - PHPIn this third installment of a four-part series, I show you that a private constructor can be truly helpful when strictly implementing the Singleton design pattern. In this case, the pattern will be applied within a class that behaves like a simple MySQL abstraction layer, but the same concept can be extended to other classes.
print this article SEARCH DEV SHED |
Provided that you already understood the rationale behind declaring the constructor of the previous MySQL driver private, it’s time to extend its current functionality. But how will this be done? Simply by our adding a few additional methods to it, the class will be able to establish a connection to the server, run queries and so forth, through a friendly interface. Having explained that, below I listed the full definition of the driver, including the extra methods that will perform the aforementioned tasks: class MySQL { private $_result = NULL; private $_link = NULL; private $_config = array(); private static $_instance = NULL;
// return Singleton instance of MySQL class public static function getInstance(array $config = array()) { if (self::$_instance === NULL) { self::$_instance = new self($config); } return self::$_instance; }
// private constructor private function __construct(array $config) { if (count($config) < 4) { throw new Exception('Invalid number of connection parameters'); } $this->_config = $config; }
// prevent cloning class instance private function __clone(){}
// connect to MySQL private function connect() { // connect only once static $connected = FALSE; if ($connected === FALSE) { list($host, $user, $password, $database) = $this->_config; if ((!$this->_link = mysqli_connect($host, $user, $password, $database))) { throw new Exception('Error connecting to MySQL : ' . mysqli_connect_error()); } $connected = TRUE; unset($host, $user, $password, $database); } }
// perform query public function query($query) { if (is_string($query) and !empty($query)) { // lazy connect to MySQL $this->connect(); if ((!$this->_result = mysqli_query($this->_link, $query))) { throw new Exception('Error performing query ' . $query . ' Message : ' . mysqli_error($this->_link)); } } }
// fetch row from result set public function fetch() { if ((!$row = mysqli_fetch_object($this->_result))) { mysqli_free_result($this->_result); return FALSE; } return $row; }
// get insertion ID public function getInsertID() { if ($this->_link !== NUlL) { return mysqli_insert_id($this->_link); } return NULL;
}
// count rows in result set public function countRows() { if ($this->_result !== NULL) { return mysqli_num_rows($this->_result); } return 0; }
// close the database connection function __destruct() { is_resource($this->_link) AND mysqli_close($this->_link); } }// End MySQL class Done. As you can see, at this point the above “MySQL” class not only exposes a single entry point through its Singleton “getInstance()” method, but it defines some simple methods for executing queries against the selected database, fetching and counting rows, and finding insertion IDs as well. Also, it’s worth noting the implementation of a method called “connect()” that takes care of connecting to MySQL in a lazy way, meaning that it’ll be run once, and only when the driver performs a given query. So far, so good. At this moment, the previous MySQL driver still isn't suitable to use in a production environment, but it definitely it looks much more functional than it did in an earlier stage. Thus, it’s time to set up an example that shows how to use it in a concrete case, so you can see how it works. This hands-on example will be coded in the last section of the tutorial. So click on the link that appears below and keep reading.
blog comments powered by Disqus |
|
|
|
|
|
|
|
