What is the need for an unsaved-value attribute in hibernate?

Question

What is the need for an unsaved-value attribute?

Answer 1

http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html/mapping.html

unsaved-value (optional - defaults to a "sensible" value): an identifier property value that indicates an instance is newly instantiated (unsaved), distinguishing it from detached instances that were saved or loaded in a previous session.

In your example, unsaved-value="null" seems pretty pointless, since I suspect the "sensible default" for a Long is null.

It's more useful for primitive types (e.g. int), which cannot be null, and the default unsaved-value of 0 may be undesirable in some applications (0 being a perfectly valid number value).