[Magento] Hiding out of stock products in advanced search results

app/code/local/Endryu/AdvancedInStockOnly/CatalogSearch/Model/Advanced.php

After creating such a file, we put there lines of code given below. getProductCollection() method does override original method from core module and has an additional rule inside (->joinField(...)), which - in fact - filters out these products in collection that has out of stock status. Moreover, we add filter to the active Website ($websiteId):

<?php

class Endryu_AdvancedInStockOnly_CatalogSearch_Model_Advanced extends Mage_CatalogSearch_Model_Advanced {

  /**
   * filters product collection via in stock only filter
   */
    public function getProductCollection(){
        if (is_null($this->_productCollection)) {
            $storeId = Mage::app()->getStore()->getId();
            $websiteId = Mage::getModel('core/store')->load($storeId)->getWebsiteId();
            $this->_productCollection = Mage::getResourceModel('catalogsearch/advanced_collection')
                ->addAttributeToSelect(Mage::getSingleton('catalog/config')
->getProductAttributes())
                ->addMinimalPrice()
                ->addTaxPercents()
                ->addStoreFilter()
                ->joinField('stock_status', 'cataloginventory/stock_status', 'stock_status', 'product_id=entity_id', array('stock_status' => Mage_CatalogInventory_Model_Stock_Status::STATUS_IN_STOCK, 'website_id' => $websiteId));
                Mage::getSingleton('catalog/product_status')
->addVisibleFilterToCollection($this->_productCollection);
                Mage::getSingleton('catalog/product_visibility')
->addVisibleInSearchFilterToCollection($this->_productCollection);
        }

        return $this->_productCollection;
    }

}

Next, we need a configuration XML file for fresh module. So we do:

app/code/local/Endryu/AdvancedInStockOnly/etc/config.xml

and fill with:

<?xml version="1.0"?>
<config>
 <global>
  <models>

   <catalogsearch>
    <rewrite>
	 <advanced>Endryu_AdvancedInStockOnly_CatalogSearch_Model_Advanced</advanced>
    </rewrite>
   </catalogsearch>

  </models>
 </global>
</config>

The last thing to do is to switch the module on by creating:

app/etc/modules/Endryu_AdvancedInStockOnly.xml

with content given below:

<?xml version="1.0"?>

<config>
 <modules>
  <Endryu_AdvancedInStockOnly>
   <active>true</active>
   <codepool>local</codepool>

  </Endryu_AdvancedInStockOnly>
 </modules>
</config>

Have fun:)