Re: [JBoss-user] a finder method that doesn't throw an exception when not found?

[Dain S. <da...@da...>]

Brian Macy wrote:
> I'm having a difficult time as several important pieces of behavior in 
> my system rely on checks against existence. Right now I just have to 
> catch the FinderException and handle it there. The problem is that it 
> appears the FinderException is occurring when there are some transient 
> database problems too.
> 
> What I need is a finder like function that returns null for not found, 
> the object if found, and throws exceptions when there are errors.

Last time I checked that is the way the EJB 2.1 spec will work. 
Unfortunately, it will not be final for a while and is targeted for 
JBoss 4.0.

> What's really hurting is that this is causing data integrity issues 
> (FinderException thrown, so I end up adding a duplicate item, which then 
> causes every finder method that assumes it is returning a single object 
> to also throw an exception). I can deal with some of this by adding 
> constraints directly to the DB but a significant reason for using J2EE 
> was to be DB independent.

You should definitely have pk constraints so you can't get dupes.

> Anyways, the death of the system ends up being:
> 
> - sudden high load on the DB
> - followed by transactions rollback (DB load stays high)
> - removing bean with tx set errors

I think Bill fixed the last one of these yesterday (or you have a bad 
custom primary key class).

> - OutOfMemory Exceptions and SQL DB running out of connections
> - If I'm lucky the system tries to shutdown
> 
> 
> Actually, maybe I just partially solved my problem. It looks like there 
> is an ObjectNotFoundException sublcassing FinderException... assuming it 
> is thrown only when a successful query is made and nothing is found I 
> should be generally ok. Still, something that returns null would be much 
> better (without having to return a Collection).

You should always get an ObjectNotFoundException when the object is not 
found and a FinderException when a real problem happens.

-dain