Collection::getIdCache

private function getIdCache()
{
	if($this->idIndex === null)
	{
		$this->idIndex = array();
		foreach($this->values as $k => $item)
		{
			$itemId = $item->getId();
			if($itemId)
			{
				$this->idIndex[$itemId] = array($k, $item);
			}
		}
	}

	return $this->idIndex;
}