/**
	 * @return MongoCursor
	 */
	public function findWhere($where)
	{
		$collection=$this->collection->find($where);
		$callback=$this;
 
		$collection->next_object=function() use ($collection, $callback)
		{
			$data=$collection->getNext();
			$obj=$callback->create_object($data);
			return ($obj);
		};
		return ($collection);
	}

	public function findOneWhere($where)
	{
		$collection=$this->findWhere($where);
		$func=$collection->next_object;
		return ($func());
	}

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
 
/**
* MY_Router Class *
* An extension to the core router class to allow controllers to be in multi-level directories.
*
* @package Router
* @version 1.0
* @author Damien K.
* @copyright Copyright (c) 2010, Ollie Rattue
* @license http://www.opensource.org/licenses/mit-license.php
* @link https://github.com/ollierattue/codeigniter-multi-level-controller-extension
*/
 
class MY_Router extends CI_Router {
 
    // --------------------------------------------------------------------
 
    /**
* OVERRIDE
*
* Validates the supplied segments. Attempts to determine the path to
* the controller.
*
* @access private
* @param array
* @return array
*/
    function _validate_request($segments)
    {
        if (count($segments) == 0)
        {
            return $segments;
        }
 
        // Does the requested controller exist in the root folder?
        if (file_exists(APPPATH.'controllers/'.$segments[0].EXT))
        {
            return $segments;
        }
 
        // Is the controller in a sub-folder?
        if (is_dir(APPPATH.'controllers/'.$segments[0]))
        {
            // @edit: Support multi-level sub-folders
            $dir = '';
 
do
            {
                if (strlen($dir) > 0)
                {
                    $dir .= '/';
                }
 
$dir .= $segments[0];
                $segments = array_slice($segments, 1);
            } while (count($segments) > 0 && is_dir(APPPATH.'controllers/'.$dir.'/'.$segments[0]));
 
  // Set the directory and remove it from the segment array
            $this->set_directory($dir);
            // @edit: END
 
            // @edit: If no controller found, use 'default_controller' as defined in 'config/routes.php'
            if (count($segments) > 0 && ! file_exists(APPPATH.'controllers/'.$this->fetch_directory().$segments[0].EXT))
            {
                array_unshift($segments, $this->default_controller);
            }
            // @edit: END
 
            if (count($segments) > 0)
            {
                // Does the requested controller exist in the sub-folder?
                if (!file_exists(APPPATH.'controllers/'.$this->fetch_directory().$segments[0].EXT))
                {
                    // show_404($this->fetch_directory().$segments[0]);
                    // @edit: Fix a "bug" where show_404 is called before all the core classes are loaded
                    $this->directory = '';
                    // @edit: END
                }
            }
            else
            {
                // Is the method being specified in the route?
                if (strpos($this->default_controller, '/') !== FALSE)
                {
                    $x = explode('/', $this->default_controller);
 
                    $this->set_class($x[0]);
                    $this->set_method($x[1]);
                }
                else
                {
                    $this->set_class($this->default_controller);
                    $this->set_method('index');
                }
 
                // Does the default controller exist in the sub-folder?
                if (!file_exists(APPPATH.'controllers/'.$this->fetch_directory().$this->default_controller.EXT))
                {
                    $this->directory = '';
                    return array();
                }
 
            }
 
            return $segments;
        }
 
        // If we've gotten this far it means that the URI does not correlate to a valid
        // controller class. We will now see if there is an override
        if (!empty($this->routes['404_override']))
        {
            $x = explode('/', $this->routes['404_override']);
 
            $this->set_class($x[0]);
            $this->set_method(isset($x[1]) ? $x[1] : 'index');
 
            return $x;
        }
 
        // Nothing else to do at this point but show a 404
        show_404($segments[0]);
    }
 
    // --------------------------------------------------------------------
 
    /**
* OVERRIDE
*
* Set the directory name
*
* @access public
* @param string
* @return void
*/
    function set_directory($dir)
    {
        $this->directory = str_replace(array('.'), '', $dir).'/'; // @edit: Preserve '/'
    }
 
    // --------------------------------------------------------------------
}

UPDATE a 
SET field1=b.field1
FROM b
WHERE b.feld2=a.field2