Ensure proper retrieval of parent entity_id

[romainruaud]

There may be inconsistency issues when retrieving relations by child when using Magento Commerce (EE).

This is due to the fact that on Magento EE, catalog_product_relation is built like this :

CREATE TABLE `catalog_product_relation` (
  `parent_id` int(10) unsigned NOT NULL COMMENT 'Parent ID',
  `child_id` int(10) unsigned NOT NULL COMMENT 'Child ID',
  PRIMARY KEY (`parent_id`,`child_id`),
  KEY `CATALOG_PRODUCT_RELATION_CHILD_ID` (`child_id`),
  CONSTRAINT `CAT_PRD_RELATION_CHILD_ID_SEQUENCE_PRD_SEQUENCE_VAL` FOREIGN KEY (`child_id`) REFERENCES `sequence_product` (`sequence_value`) ON DELETE CASCADE,
  CONSTRAINT `CAT_PRD_RELATION_PARENT_ID_CAT_PRD_ENTT_ENTT_ID` FOREIGN KEY (`parent_id`) REFERENCES `catalog_product_entity` (`row_id`) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='Catalog Product Relation Table' 

Notice the reference between parent_id and row_id.

This would lead to inconsistency when retrieving parent_id.

Regards