Database access class

DB.class.php

<?php

/**
 * Database access class
 * 
 * @author sag
 */

class DB {
    
    /**
     * Collection of database connections
     * @var Array connections collection
     */
    protected static $_instance = array();
    
    /**
     * Current database connection object
     * @var PDO connection object
     */
    public $conn;
    
    /**
     * Creates connection by given alias (implements singleton)
     * @param String $alias Database connection alias
     */
    private function __construct($alias){
		$cfg = Config::getInstance();
		$connString = $cfg->get("db.".$alias.".connString");
		$user = $cfg->get("db.".$alias.".user");
		$pass = $cfg->get("db.".$alias.".pass");
		try{
			$this->conn = new PDO($connString, $user, $pass, array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES UTF8"));
		} catch (PDOException $e) {
			return null;
		}
    }

    private function __clone(){}
    
    /**
     * Getting Database connection instance by alias (implements Singleton)
     * @param String $alias Database connection alias
     * @return PDO connection object
     */
    public static function getInstance($alias = "serv"){
		if (empty(self::$_instance[$alias])) {
			try {
				self::$_instance[$alias] = new self($alias);
			} catch (PDOException $e) {
				return null;
			}
		}
		return self::$_instance[$alias];
    }

	/**
	 * Execute 'SELECT-type' SQL-query by query alias (SQL-queries are stored in static class DBQuery)
	 * @param String $queryAlias SQL-query alias (= DBQuery key)
	 * @param Array $params Associative array with parameters for binding in prepared statement
	 * @param Mixed $fetchTo Type of return value. Could be object, class name or empty (to fetch into stdClass object)
	 * @param Array $constr Array of parameters to pass to new Class instance constructor
	 * @throws Exception
	 * @return Mixed result depending on $fetchTo parameter
	 */
    public function query($queryAlias, $params = null, $fetchTo = null, $constr = null) {

		if (!$this->conn)
			throw new Exception ("Database connection error");

		// getting query by alias
		$query = DBQuery::getQuery("get.".$queryAlias);

		if (!empty ($params)) {
			// replacing array parameters to IN-statement (exmpl: WHERE value IN ('1','3','5') )
			foreach ($params as $param => $value) {
				if (is_array($value)) {
					$query = str_replace(':'.$param, "'".implode("', '", $value)."'", $query);
					unset($params[$param]);
				}
			}
		}

		// creating prepared statement
		$stmt = $this->conn->prepare($query);
		if (!empty ($params)) {
			// binding parameters to prepared statement
			foreach ($params as $param => $value) {
				$type = null;
				if (is_int($value)) 	$type = PDO::PARAM_INT;
				if (is_string($value)) 	$type = PDO::PARAM_STR;
				if (!is_array($value)) 	$stmt->bindValue($param, $value, $type);
			}
		}
		// executing statement
		if (!@$stmt->execute()) {
			throw new Exception("Invalid SQL-query or wrong parameters");
		}

		// fetching result
		if (!empty($fetchTo)) {
			if (is_string($fetchTo)) {			// $fetchTo is a class name
				$stmt->setFetchMode(PDO::FETCH_CLASS, $fetchTo, $constr);
			} elseif (is_object($fetchTo)) {	// $fetchTo is an object
				$stmt->setFetchMode(PDO::FETCH_INTO, $fetchTo);
			}
		} else {	// $fetchTo is empty
			$stmt->setFetchMode(PDO::FETCH_OBJ);
		}
		return $stmt->fetchAll();

    }

	/**
	 * Execute 'INSERT/UPDATE/DELETE-type' SQL-query by alias (SQL-queries are stored in static class DBQuery)
	 * @param String $queryAlias SQL-query alias (= DBQuery key)
	 * @param Array $params Associative array with parameters for binding in prepared statement
	 * @throws Exception
	 * @return int Amount of updated/deleted/inserted records
	 */
    public function exec($queryAlias, $params = null) {

		if (!$this->conn)
			throw new Exception ("Database connection error");

		//getting SQL-query
		$query = DBQuery::getQuery("set.".$queryAlias);

		// creating prepared statement
		$stmt = $this->conn->prepare($query);

		if (!empty ($params)) {
			// binding parameters
			foreach ($params as $param => $value) {
				$value = strip_tags($value);
				$stmt->bindValue($param, $value);
			}
		}

		// executing statement
		if (!@$stmt->execute())
			throw new Exception("Invalid SQL-query or wrong parameters");

		return $stmt->rowCount();
		
    }
    
}