Sometimes, you want the Database to do some computation for you rather than in the JVM, you might also create some kind of virtual column. You can use a SQL fragment (aka formula) instead of mapping a property into a column. This kind of property is read only (its value is calculated by your formula fragment).

@Formula("obj_length * obj_height * obj_width")
public long getObjectVolume()

The SQL fragment can be as complex as you want and even include subselects.