Product Top Category

This module adds an automatic field called "Product Top Category" to product categories and to products. For any category, Odoo walks up the category tree and stores the highest-level parent category it finds; if a category has no parent, it is its own top category.

On the product category form, the new field appears right after the "Parent Category" field, so users can see the top category of the category they are editing. On products, the same information is pulled automatically from the product's category, so each product also carries its top category.

Because the value is stored and recalculated when the parent category changes, it stays up to date without manual work. The module does not add menus, buttons, reports or scheduled jobs by itself; it simply makes the top-level category available for grouping, filtering and reporting, for example in sale reports.

It only makes sense if your category hierarchy has several levels: if every category sits directly under "All", the top category will always be "All" and the field brings no extra information. It touches the product.category and product.template models.