Q: Set default category I would like to set a category by default to one product because we can find it in several categories. eg: In Apple > iPhone et in Smartphones. How I could do that please?

A: You can write a code on event "catalog_product_save_after" and with the help of this event you can call a method which will call when you save any product.
In this method you can put your code which will get and check the product category. If no category is available then set your category and save product again.
