Do not show out of stock products in Magento

1. Magento Inventory Tables:

Magento uses several tables to manage stocks. Table cataloginventory_stock is used to manage stock names. Table cataloginventory_stock_item has the relationship between product and stock name. You can check table cataloginventory_stock_status to know the product's stock status. Here i have a question: Can magento index process help stock cases as well?

2.Apply stock status to product collection using event hook;

<catalog_product_collection_load_after>
                <observers>
                    <inventory>
                        <class>cataloginventory/observer</class>
                        <method>addStockStatusToCollection</method>
                    </inventory>
                </observers>
</catalog_product_collection_load_after>

    public function addStockStatusToCollection($observer)
    {
        $productCollection = $observer->getEvent()->getCollection();
        if ($productCollection->hasFlag('require_stock_items')) {
            Mage::getModel('cataloginventory/stock')->addItemsToProducts($productCollection);
        } else {
            Mage::getModel('cataloginventory/stock_status')->addStockStatusToProducts($productCollection);
        }
        return $this;
    }

    public function addStockStatusToProducts($productCollection, $websiteId = null, $stockId = null)
    {
        if ($stockId === null) {
            $stockId = Mage_CatalogInventory_Model_Stock::DEFAULT_STOCK_ID;
        }
        if ($websiteId === null) {
            $websiteId = Mage::app()->getStore()->getWebsiteId();
            if ((int)$websiteId == 0 && $productCollection->getStoreId()) {
                $websiteId = Mage::app()->getStore($productCollection->getStoreId())->getWebsiteId();
            }
        }
        $productIds = array();
        foreach ($productCollection as $product) {
            $productIds[] = $product->getId();
        }

        if (!empty($productIds)) {
            $stockStatuses = $this->_getResource()->getProductStatus($productIds, $websiteId, $stockId);
            foreach ($stockStatuses as $productId => $status) {
                if ($product = $productCollection->getItemById($productId)) {
                    $product->setIsSalable($status);
                }
            }
        }

        /* back compatible stock item */
        foreach ($productCollection as $product) {
            $object = new Varien_Object(array('is_in_stock' => $product->getData('is_salable')));
            $product->setStockItem($object);
        }

        return $this;
    }

    public function getProductStatus($productIds, $websiteId, $stockId = 1)
    {
        if (!is_array($productIds)) {
            $productIds = array($productIds);
        }

        $select = $this->_getReadAdapter()->select()
            ->from($this->getMainTable(), array('product_id', 'stock_status'))
            ->where('product_id IN(?)', $productIds)
            ->where('stock_id=?', $stockId)
            ->where('website_id=?', $websiteId);
        return $this->_getReadAdapter()->fetchPairs($select);
    }

3. Specific case for group product:

In class Mage_CatalogInventory_Model_Mysql4_Indexer_Stock_Grouped, let me put our minds on following method:

    protected function _getStockStatusSelect($entityIds = null, $usePrimaryTable = false)
    {
        $adapter  = $this->_getWriteAdapter();
        $idxTable = $usePrimaryTable ? $this->getMainTable() : $this->getIdxTable();
        $select   = $adapter->select()
            ->from(array('e' => $this->getTable('catalog/product')), array('entity_id'));
        $this->_addWebsiteJoinToSelect($select, true);
        $this->_addProductWebsiteJoinToSelect($select, 'cw.website_id', 'e.entity_id');
        $select->columns('cw.website_id')
            ->join(
                array('cis' => $this->getTable('cataloginventory/stock')),
                '',
                array('stock_id'))
            ->joinLeft(
                array('cisi' => $this->getTable('cataloginventory/stock_item')),
                'cisi.stock_id = cis.stock_id AND cisi.product_id = e.entity_id',
                array())
            ->joinLeft(
                array('l' => $this->getTable('catalog/product_link')),
                'e.entity_id = l.product_id AND l.link_type_id=' . Mage_Catalog_Model_Product_Link::LINK_TYPE_GROUPED,
                array())
            ->joinLeft(
                array('le' => $this->getTable('catalog/product')),
                'le.entity_id = l.linked_product_id',
                array())
            ->joinLeft(
                array('i' => $idxTable),
                'i.product_id = l.linked_product_id AND cw.website_id = i.website_id AND cis.stock_id = i.stock_id',
                array())
            ->columns(array('qty' => new Zend_Db_Expr('0')))
            ->where('cw.website_id != 0')
            ->where('e.type_id = ?', $this->getTypeId())
            ->group(array('e.entity_id', 'cw.website_id', 'cis.stock_id'));

        // add limitation of status
        $psExpr = $this->_addAttributeToSelect($select, 'status', 'e.entity_id', 'cs.store_id');
        $psCond = $adapter->quoteInto($psExpr . '=?', Mage_Catalog_Model_Product_Status::STATUS_ENABLED);

        if ($this->_isManageStock()) {
            $statusExpr = new Zend_Db_Expr('IF(cisi.use_config_manage_stock = 0 AND cisi.manage_stock = 0,'
                . ' 1, cisi.is_in_stock)');
        } else {
            $statusExpr = new Zend_Db_Expr('IF(cisi.use_config_manage_stock = 0 AND cisi.manage_stock = 1,'
                . 'cisi.is_in_stock, 1)');
        }

        $stockStatusExpr = new Zend_Db_Expr("LEAST(MAX(IF({$psCond} AND le.required_options = 0, i.stock_status, 0))"
            . ", {$statusExpr})");

        $select->columns(array(
            'status' => $stockStatusExpr
        ));

        if (!is_null($entityIds)) {
            $select->where('e.entity_id IN(?)', $entityIds);
        }

        return $select;
    }