Please, in my domain model I have two persistent entities "Cart" and "Product", I want to subtract the number of quantity( "Cart") from quantity ("Product") so that when I sell a product it will automatically subtract and update the product table.
I tried the math unit and also read the tutorials on https://my.webratio.com/learn/learningobject/how-to-use-math-unit, but it's not working.
I really need help with this.
Thank you.