Create a singleton class in PHP 5.3 that can connect, store, and retrieve data t

Question

Create a singleton class in PHP 5.3 that can connect, store, and retrieve data to/from a MySQL database.

Explanation / Answer

/** * PHP5 MySQL Database Class implementing the Singleton Design Pattern * * Usage: * $wjdb = wjdb::instance(); * $wjdb->connect(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME); * $results = $wjdb->query("SELECT * FROM example_db WHERE id = 1"); * $db->close(); * * @package WJ_Tutorials * @author Chris Strosser * @link http://webjawns.com/ */ class wjdb { /** * The wjdb database object * * @access private * @var object */ private $wjdb; /** * MySQLi database object * * @access private * @var object */ private static $instance; /** * Current result set * * @access private * @var object */ private $result; /** * The last result (processed) * * @access private * @var array */ private $last_result; /** * The number of rows from last result * * @access private * @var int */ private $row_count; /** * Last error * * @access private * @var string */ private $last_error; /** * PHP5 Constructor * * Making this function 'private' blocks this class from being directly created. * * @access private */ private function __construct() { } /** * Creates and references the wjdb object. * * @access public * @return object MySQLi database object */ public static function instance() { if ( !self::$instance ) self::$instance = new wjdb(); return self::$instance; } /** * Connect to the MySQL database. * * @param string $host MySQL hostname * @param string $user MySQL username * @param string $password MySQL password * @param string $name MySQL database name * @return bool True if successful, false on error. */ public function connect($host, $user, $password, $name) { // Connect to the database $this->wjdb = new mysqli($host, $user, $password, $name); // Check connection if ( mysqli_connect_errno() ) { $this->last_error = mysqli_connect_error(); return false; } return true; } /** * Checks for errors. * * @return string|false $last_error if it exists or false if no errors. */ public function is_error() { if ( isset($this->last_error) && !empty($this->last_error) ) return $this->last_error; return false; } /** * Close active connection to MySQL database. * * @access public * @return bool Always returns true. */ public function close() { if ( $this->wjdb ) $this->wjdb->close(); return true; } /** * Executes query and returns results. * * @access public * @param string $sql The SQL statement to execute. * @return mixed */ public function query($sql) { $this->result = $this->wjdb->query($sql); return $this->result; } public function get_results($sql) { if ( !$this->query($sql) ) return false; $num_rows = 0; while ( $row = $this->result->fetch_object() ) { $this->last_result[$num_rows] = $row; $num_rows++; } $this->result->close(); return $this->last_result; } public function num_rows() { return (int) $this->row_count; } /** * Retrieve a single row from the database. * * Do not include LIMIT 1 on the end, as this will be taken care * of automatically. * * @param string $sql The SQL statement to execute. * @return object The MySQL row object */ public function get_row($sql) { if ( !$results = $this->query($sql . " LIMIT 1") ) return false; return $results->fetch_object(); } /** * Sanitizes data for safe execution in SQL query. * * @access public * @param mixed $data The data to be escaped. * @return mixed */ public function escape($data) { return $this->wjdb->real_escape_string($data); } /** * Prevent cloning of wjdb. * * @access public * @return void */ public function __clone() { // Issue E_USER_ERROR if clone is attempted trigger_error('Cloning wjdb is prohibited.', E_USER_ERROR); } /** * Destructor * * @access public */ public function __destruct() {} }

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