Hibernate version: 2.1.6

Mapping documents:

Code between sessionFactory.openSession() and session.close():

Full stack trace of any exception that occurs:

Name and version of the database you are using:PostgreSQL7.2

Debug level Hibernate log excerpt:

Hi!
I have the following scenario: a user wants to register. He/She must enter a login and a password. The login must be unique. How can I garantee this? I read in "Hibernate in action" (Page 172 - CHAPTER 5) that there are two ways:

1- lock held in memory: achieved by using the synchronized java keyword?
2- lock table in the database;

How can I implement number 2 in the specified scenario?

Thanks a million!
M

Use a unique constraint?

OK, this is a very good and simple idea. But I have one more doubt. When two users try to register the same login, one of them will get a success page and the other will get a fail (horrible) page. This fail page will have an HibernateException with a SQL unique constraint violation error. I can not show this to my user. I have to show a "beautiful" message stating that a user with that login already exists. So, here is the question: how do I know that the HibernateException was caused by a unique constraint error in the login column?
Thanks again!
M

The Hibernate JDBCException wraps the underlying SQLException. Check the JavaDoc.

Thanks, I will check the SQLState, errorCode and message in the SQLException.
By the way, is there a database independent way of doing this check, such as:
?

Thank you SO MUCH! :o)
M

Yes, there is Spring, which has a converter utility from SQLException to a typed exception hierarchy. Good uses of this are rare, as database exceptions should be non-recoverable (LockFailedException _should_ be recoverable).

This means that your idea works for simple errors such as a unique contraint violation, but falls over if constraints (and business rules) get more complex. In this case, you'd need a validation layer in your application anyway and feed the database only clean/checked values to avoid any exception.

Some databases have native features to evalute "CHECK" or to add "input mask" , it can be used for validation. Probably you can find or implement custom validator for popular MVC frameworks.

Hi,
Thanks for the tips. So, I have 3 options:
1- Check if the SQLException was generated because of a unique constraint error;
2- Use a validation layer in my application to check duplicate logins before adding the use to the system. In this case, how would such a validation be performed? I have many concurrent threads accessing my application, so I need some sort of locking (java synchronized keyword or database table lock) so that 2 or more users aren't inserted in the database with the same login at the same time;
3- Use some sort of database validation (CHECK) to verify if another user exists with the same login. This solution looks good, however I am discarding it for now because I want to be as database neutral as I can.

I still don't know how to implement option 2. Any sugestions?

Thanks,
M

option "1" is better if you need user friendly output and performance,there is standard "sqlstate" code, google must help to find it or try to reproduce and print it.

Thanks everybody!

M