Php 如何根据magento中的库存状态对产品集合进行排序

我想在分类页面上对产品集合进行排序，以便库存产品出现在缺货产品之前。所有缺货产品将显示在库存产品之后。我已经重写了Mage_Product_Block_列表块

You can use catalog_product_collection_load_before event.   
And in the observer:

public function modifyProductCollection(Varien_Event_Observer $observer) {
    //catalog_product_collection_load_before
    $collection = $observer->getCollection();

    $collection->getSelect()->joinLeft(
                array('_inventory_table' => $collection->getTable('cataloginventory/stock_item')),
                "_inventory_table.product_id = e.entity_id",
                array('is_in_stock')
            )
            ->order('is_in_stock DESC')
            ->order('created_at DESC');
}