I've been trying to understand, How Magento is managing the category_ids attribute for product in database and on code level? I noticed this attribute is handled in a different way to the other static backend_type eav attributes.
If someone has already got chance to analyze it, his finding can save time for me. Thanks
This isn't a static attribute, this a relation between two entities and it's stored in the catalog_category_product table. The model related is \Magento\Catalog\Model\CategoryLink
Take a look at \Magento\Catalog\Model\ResourceModel\Product, you can see the getCategoryIds method that calls \Magento\Catalog\Model\ResourceModel\Product\CategoryLink::getCategoryLinks
