David Sims wrote:
> Myls Jeffery wrote:
> > We have a requirement for a number of static data types in our project.
> > Each type of static data will be provided by a read-only entity bean. I
> > want to ensure that only one instance of an entity bean is created so that
> > we do not have multiple entity beans of the same type polling the database
> > for the same data.
> >
> > To accomplish this, I was thinking of creating a PK class for each entity
> > bean that no matter what ID you pass to it it will treat it as the same.
> > Therefore the EJB server will not create a new instance of the entity bean -
> > it will simply return the existing one.
>
> I've done this very thing in the past. Home.findByPrimaryKey() always
> ignored the PK that was passed in and instead "found" the same PK every
> time. You should be able to do the same thing with Home.create().
>
> In the situation I was in, we needed a "singleton", so this was the
> strategy we took. Worked out fine. It was a portable, EJB primary key
> generator that was part of the Enterprise Tool Kit.
>
Maybe I miss something, but if you really implemented a singleton this way, then I
won't ever buy your product :-(
First of all, EJBs are intended to be distributed. This means that if your servers
are clustered, you can't have a real singleton (only a singleton per VM) for all
your servers. The only way to have a real singleton is to break out of the EJB
model and to implement, for example, a CORBA singleton.
Second, even if you use a single container, this container might instantiate
several instances of the same entity bean (i.e. the same PK). In fact, all the
servers I've used, except Weblogic, use one instance of the same Entity Bean per
concurrent transaction.
Do I miss something?
JB.
>
> That's not much information, but I hope it helps.
>
> cheers,
> david
>
> --
> David Sims [EMAIL PROTECTED]
> Sims Computing, Inc. www.simscomputing.com
>
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