Generated properties are properties that have their values generated by the database. Typically, Hibernate applications needed to
refresh objects that contain any properties for which the database was generating values. Marking properties as generated, however, lets the application delegate this responsibility to Hibernate. When Hibernate issues an SQL INSERT or UPDATE for an entity that has defined generated properties, it immediately issues a select afterwards to retrieve the generated values.
never (the default): the given property value is not generated within the database.
always: the property value is generated both on insert and on update.