How to reindex catalog_category_product_index for single entity?

[Tomasz-Silpion]

Summary (*)

There are a lot references in code to catalog_category_product_index action like catalogProductSave or catalogProductMassAction which seem to be obsolete as they are no longer called anywhere https://github.com/OpenMage/magento-lts/blob/main/app/code/core/Mage/Catalog/Model/Resource/Category/Indexer/Product.php or in https://github.com/OpenMage/magento-lts/blob/main/app/code/core/Mage/Catalog/Model/Resource/Product.php#L300 refreshIndex method.

Possibly, both of them can be marked as deprecated as Mage_Catalog_Model_Resource_Category_Indexer_Product _refreshRootRelations ends with FK_CAT_CTGR_PRD_IDX_CTGR_ID_CAT_CTGR_ENTT_ENTT_ID exception due try to insert category_id 0 as given in fresh installed core_store_group.store_id join and the Mage_Catalog_Model_Resource_Product refreshIndex function breaks on non existing $categoryObject->refreshProductIndex($indexCategoryIds, $indexProductIds); call.

Examples (*)

Call

Mage::getResourceModel('catalog/category_indexer_product')->catalogProductMassAction($event);

SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`catalog_category_product_index`, CONSTRAINT `FK_CAT_CTGR_PRD_IDX_CTGR_ID_CAT_CTGR_ENTT_ENTT_ID` FOREIGN KEY (`category_id`)

or

Mage::getResourceModel('catalog/product')->refreshIndex($product);

Call to undefined method Mage_Catalog_Model_Resource_Category::refreshProductIndex()

Proposed solution

1. refreshProductIndex method should be added to Mage_Catalog_Model_Resource_Category class
2. Entire method, second half or at least insertFromSelect method should be removed from https://github.com/OpenMage/magento-lts/blob/main/app/code/core/Mage/Catalog/Model/Resource/Category/Indexer/Product.php#L739 _refreshRootRelations function.
3. Both catalogProductMassAction and refreshIndex should be marked as deprecated.