Connecting to second database not working in CodeIgniter

Question

Im trying to intergrate phpbb3 with code igniter. im pretty successful but im tryying to access the forum database and it not working. This is currently what I have in my database file.

/** FORUM DATABASE **/

$active_group = 'forum';
$active_record = TRUE;

$db['forum']['hostname'] = 'localhost';
$db['forum']['username'] = 'root';
$db['forum']['password'] = 'root';
$db['forum']['database'] = 'phpbb';
$db['forum']['dbdriver'] = 'mysqli';
$db['forum']['dbprefix'] = 'phpbb';
$db['forum']['pconnect'] = FALSE;
$db['forum']['db_debug'] = TRUE;
$db['forum']['cache_on'] = FALSE;
$db['forum']['cachedir'] = '';
$db['forum']['char_set'] = 'utf8';
$db['forum']['dbcollat'] = 'utf8_general_ci';
$db['forum']['swap_pre'] = '';
$db['forum']['autoinit'] = TRUE;
$db['forum']['stricton'] = TRUE;

/** CMS DATABASE **/
$active_group = 'default';
$active_record = TRUE;

$db['default']['hostname'] = 'localhost';
$db['default']['username'] = 'root';
$db['default']['password'] = 'root';
$db['default']['database'] = 'cms';
$db['default']['dbdriver'] = 'mysql';
$db['default']['dbprefix'] = '';
$db['default']['pconnect'] = FALSE;
$db['default']['db_debug'] = TRUE;
$db['default']['cache_on'] = FALSE;
$db['default']['cachedir'] = '';
$db['default']['char_set'] = 'utf8';
$db['default']['dbcollat'] = 'utf8_general_ci';
$db['default']['swap_pre'] = '';
$db['default']['autoinit'] = TRUE;
$db['default']['stricton'] = TRUE;

And here is a method that is trying to access the database. It keeps returning null.

public function getUserGroupMembership()
{
  $forum = $this->load->database('forum',TRUE);
  global $table_prefix;
  $userId = $this->_user->data['user_id'];
  $this->forum->select('g.group_name');
  $this->forum->from($table_prefix . 'groups g');
  $this->forum->from($table_prefix . 'user_group u');
  $this->forum->where('u.user_id', $userId);
  $this->forum->where('u.group_id', 'g.group_id', FALSE);
  $query = $this->forum->get();
  foreach ($query->result_array() as $group)
  {
      $groups[] = $group['group_name'];
  }
  return $groups;
}

Answer 1

The database object is loaded in the $forum variable, but the $this->forum variable is used to interact with the database. It's not going to work as $forum is a local variable and $this->forum is an class variable, they aren't the same. To fix your code, you should change $forum to $this->forum or $this->forum to $forum. You can not use both at the same time.