Hi;

The book "Hibernate in Action" uses Long for the PK. However, I have used long and it works fine. Is there an advantage to using Long?

thanks - dave

Long allows you to have NULL values.

Yes, but it is used for PKs and AFAIK you cannot have a NULL PK

??? - thanks - dave

You're right, BUT you only talk about objects which are already in the database (persistent objects) and have a primary key. Objects can also be transient - when they are created (Object o = new Object()). In this case they usually have no primary key (except for the situation the key is assigned manually and not by the database) and they are marked being transient using the XML attribute "unsaved-value". This can be NULL in case of a Long and must be another value for long, since a long cannot be NULL.

I think there is also information about this (transient and persistent state) in the documentation and HiA book.

Best regards
Sven

OOOOOOOOOOOOOH

That makes a lot of sense. (That's why I ask questions like this - a lot of time there is a very good reason to do it that way.)

thanks - dave

Just a suggestion. The above posting was helpful so mark his post as helpful. Its good feedback and rewards posters in a small way.

I dont think this is the main reason since long can just have unsaved as 0, so it works similarly, especially if you have a native key which starts above 0. If you are putting your ID as the key of a Map, or passing it to methods that take Object as an input, then the long type will need to be constantly wrapped and unwrapped, but the Long one is already there. Its not a ton of overhead, but for performance nuts, reducing the number of instances created matters.

Chris