public static function addUserToGroup($user_id, $group_id)
	{
		// Get the user's existing entries
		$entries = self::all()
			->whereEquals('user_id', $user_id)
			->rows();

		$existing = array();
		foreach ($entries as $entry)
		{
			$existing[] = $entry->get('group_id');
		}

		$group_id = (is_array($group_id) ? $group_id : array($group_id));

		$blank = self::blank();

		// Loop through groups to be added
		foreach ($group_id as $group)
		{
			$group = intval($group);

			// Is the group already an existing entry?
			if (in_array($group, $existing))
			{
				// Skip.
				continue;
			}

			$query = $blank->getQuery()
				->insert($blank->getTableName())
				->values(array(
					'user_id'  => $user_id,
					'group_id' => $group
				));

			if (!$query->execute())
			{
				return false;
			}
		}

		return true;
	}