Clearing product collection in Product Listing without images - Magento 1.9

Question

In our Magento project we have around 200 thousand skus and many of them are with incomplete information. So we made a filter to prevent products without images from appearing on the category pages.

<catalog_product_collection_load_before>
    <observers>
        <mymodel_catalog_product_collection_load_before_clean_images>
            <type>singleton</type>
            <class>mymodel/observer</class>
            <method>filterProductsWithoutImages</method>
        </mymodel_catalog_product_collection_load_before_clean_images>
    </observers>
</catalog_product_collection_load_before>

...

public function filterProductsWithoutImages($observer) {
    if (isset($observer['collection'])) {
        $collection = $observer['collection'];
        $collection->addAttributeToFilter('small_image', array('neq' => "no_selection"));

        return $this;
    }
}

Products without images are removed from the collection. The problem occurs with pagination. The filtered products generate "holes" in the product listing. Example:

Category Accessories: 100 SKUS active.

Page 1: 36 products. Only 20 products are displayed, because 16 are without images.

Page 2: 36 products. Only 9 products are displayed, because 27 are without images.

Page 3: 28 products. The 28 products are displayed because they all have images.

So the problem is that after changing the collection, either through events catalog_product_collection_load_before or catalog_product_collection_load_after, the collection's pagination is not updated and the indices of the filtered products remain.

My questions:

1. In my understanding, the page was built after the load of the collection (so I was using the catalog_product_collection_load_before event). But because of this situation, it does not seem to be that way. How does it actually work?

2. Considering that if I edit the collection and load it again it can generate an infinite loop, how can I update the collection so as not to generate these "holes"?

Answer 1

Try controlling the collection filtering via extending the Block_Product_List_Toolbar, this has worked for me on similar scenario to you. Here's some code to get you started;

config.xml (in <global> scope):

<blocks>
  <catalog>
      <rewrite>
          <product_list_toolbar>YourCompany_YourModule_Block_Product_List_Toolbar</product_list_toolbar>
      </rewrite>
  </catalog>
</blocks>

YourModule/Block/Product/List/Toolbar.php:

<?php
class YourCompany_YourModule_Block_Product_List_Toolbar extends Mage_Catalog_Block_Product_List_Toolbar
{

    public function setCollection($collection)
    {
       parent::setCollection($collection);

       $this->getCollection()->addAttributeToFilter('small_image', array('neq' => "no_selection"));

       return $this;
    }

}