Collection in Event Observer: Using parentId from simple product to remove configurable product

Question

I have a category where I want to display only those configurable products, which have simple products with some specific sizes. If the configurable product does not have a simple product with the required size, it should not show up. I use the catalog_product_collection_load_after event in order to avoid problems with the pagination and layered navigation.

The observer is working and I am able to get the option values of the attached simple products, but I am unable to remove the parent configurable products dynamically if it has no simple product with the required size - it is working if I hardcode the parentId though. This is my function:

public function getPlusSizeProducts(Varien_Event_Observer $observer)
{
    $collection = $observer->getEvent()->getCollection();
    $plusSizes = array('59', '128'); // Show configurable products which have simple products with these sizes/option ids
    $availableSizes = array();
    $parentIds = array();

    if ($collection instanceof Mage_Catalog_Model_Resource_Product_Type_Configurable_Product_Collection)
    {
        foreach($collection->getItems() as $item)
        {
            $availableSizes[] = $item->getProductSize();    // Get option ids from product
            if (count(array_intersect($plusSizes, $availableSizes)) == 0 )
            {
                $parentIds[] = $item->getParentId();
                $collection->removeItemByKey($item->getParentId()) // does nothing
            }
        }
    }
    $collection->removeItemByKey($parentIds[0]) // does nothing, array is empty
}

How can I remove the configurable products using parentId?

Ideally I'd also like to use the catalog_product_collection_load_before event to apply some filters on the collection upfront, but I always get a 500 internal server error when trying to load the collection with ->load();

I appreciate anything which points me into the right direction =)

---

EDIT: Based on Marius answer I modified my code, but I still can't get it to work. I am unable to get the parent ids into one single array outside the loop (even though it is defined there) - which is what I need based on my understanding. Instead the function creates a $parentIds array for every product in the collection.

Answer 1

I see two problems in your code:

1. The whole if-block is never executed.

   if ($collection instanceof Mage_Catalog_Model_Resource_Product_Type_Configurable_Product_Collection)
   

This would be a collection of product type objects, not of products. There is no class for a "collection of configurable products", you have a collection of products and will need to check the type of each product (by getProductType(), not by class name) on its own.

1. To construct $availableSizes you will need a second loop over the child products. Also, you have to initialize it within the outer loop.

Answer 2

I think the problem is the way you keep the $parentId.
You loop through all the items in the collection. This means that the $parentId will always have the value of the last parent id found in the collection.
So, when calling $collection->removeItemByKey($parentId); you only remove the last parent id from the collection.

Just make sure that $item->getParentId() get's the value you need, and save it in an array so you can remove all of them that don't fit your needs.