php - Magento get a product collection in an arbitrary order

Question

I have developed a custom search engine for our Magento store and I am trying to load the product collection in a very specific order (I have ranked the results according to an algorithm I designed).

I can load the product collection correctly, however it is not in the order that I would like it to be in. Here is basically how it is working now:

My database query basically comes back with a PHP array of product IDs. For this example lets say it looks like this:

$entity_ids = array(140452, 38601 );

Now I can transpose the 140452 and the 38601 and the product collection comes back in the same order each time. I would like the product collection to be in the same order as the ID of the entity ids.

The code I am using to create my collection is as follows:

$products = Mage::getModel('catalog/product')
    ->getCollection()
    ->addAttributeToSelect('*')
    ->addAttributeToFilter('entity_id', array('in' => $entity_ids))
    ->setPageSize($results_per_page)
    ->setCurPage($current_page)
    ->load();

Is there a way to set the sort order to be the order of the $entity_ids array?

Answer 1

Collections inherit from the class

Varien_Data_Collection_Db

There's a method named addOrder on that class.

public function addOrder($field, $direction = self::SORT_ORDER_DESC)
{
    return $this->_setOrder($field, $direction);
}

So, you'd think something like this should work for basic ordering

Mage::getModel('catalog/product')
->getCollection()
->addAttributeToSelect('*')
->addOrder('entity_id');

However, it doesn't. Because of the complex joining involved in EAV Collections, there's a special method used to add an attribute to the order clause

Mage_Catalog_Model_Resource_Eav_Mysql4_Product_Collection::addAttributeToSort

However again, this can only be used to add simple attributes. To create an arbitrary sort, you'll need to manipulate the Zend_Select object directly. I'm not a big fan of this, and I'm not a big fan of using custom mysql functions to achieve things, but it appears it's the only way to do this

I tested the following code on a stock install and got the desired results. You should be able to use it to get what you want.

        $ids = array(16,18,17,19);
        $products = Mage::getModel('catalog/product')->getCollection()
        ->addAttributeToSelect('*')
        ->addAttributeToFilter('entity_id',$ids);           

                    //shakes fist at PDO's array parameter
                    $ids = array_map('intval', $ids);
        $products->getSelect()->order("find_in_set(e.entity_id,'".implode(',',$ids)."')");
        foreach($products as $product)
        {
            var_dump($product->getEntityId());
            var_dump($product->getSku());
        }