I think before people go breaking the contracts laid out by the
specification they should quantify the performance gains from doing so.
> -----Original Message-----
> From: A mailing list for Enterprise JavaBeans development
> [mailto:[EMAIL PROTECTED]]On Behalf Of Richard Monson-Haefel
> Sent: Thursday, May 25, 2000 5:20 AM
> To: [EMAIL PROTECTED]
> Subject: Re: ejbFindByPrimaryKey & Database lookup
>
>
> While I agree that simply returning the primary key is more
> efficient then checking
> for the entity in the database, there are drawbacks to this strategy.
>
> Here is the problem: If the entity doesn't exist in the database
> then the activated
> instance will throw an exception in its ejbLoad method which will
> result in a
> transaction rollback.
>
> This rollback is avoided with the ejbFind method that checks for
> the entity, because
> it throws an application exception (ObjectNotFoundException),
> which doesn't cause a
> transaction rollback. Generally we don't expect the ejbFind
> method to cause a
> transaction rollback if there is no entity is found. In
> addition, the contract of
> the find operation is broken. Instead of throwing an
> ObjectNotFoundException, as
> expected, the find method will throw a RemoteException.
>
> As long as the bean developer and application developer are aware of these
> differences the change in behavior (which does not conform with
> the specification)
> is perhaps tolerable.
>
> Richard
> --
> Richard Monson-Haefel
> Author of Enterprise JavaBeans, 2nd Edition
> Published by O'Reilly & Associates
> http://www.EjbNow.com
>
> David Pinnington - Sun UK - Consultant wrote:
>
> > I personally do exactly this.
> >
> > If you image the finder method actually doing a database lookup
> then you will be
> > doing the following:
> >
> > ejbFindByPrimaryKey() - does database lookup (SELECT)
> > if Entity Bean not loaded into server then
> > create new EJB inmemory and populate using ejbLoad - (SELECT)
> >
> > So in this case you have done 2 database lookups which i think
> is much more
> > expensive. The EJB clinet will still get the FinderException
> whichever way you
> > do it so I always go with the finder simply returning the PK
> without doing a
> > lookup.
> >
> > In fact I would go one step further - if ever I have a finder
> method (primary
> > key or not) where I can get / calculate the primary key withough doing a
> > database lookup I will (e.g. composite key etc).
> >
> > davep
> >
> > >
> > > Hi,
> > >
> > > I just saw a bea slide which recommends to implement
> ejbFindByPrimaryKey by
> > > just returning the parameter:
> > >
> > > String ejbFindByPrimaryKey(String pk)
> > > {
> > > return pk;
> > > }
> > >
> > > This code does not perfom a database lookup.
> > >
> > > The above coding has consequences:
> > > 1. if a bean with the specified pk does not exist,
> ejbFindByPrimaryKey will
> > > not throw a FinderException. Instead, ejbLoad will fail (in
> which case a
> > > FinderException can be thrown).
> > > 2. No database lock is set to the tuple with the pk.
> > >
> > > Has someone out there experiences with the optimized code?
> > >
> > > Thanks,
> > > Marc Volz
> > > TLC, Germany
> > >
> > >
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> > >
> >
> > ----------------------------------
> > Dave Pinnington - Sun Microsystems
> > [EMAIL PROTECTED]
> > tel: +44 (0)1223 418868
> > fax: +44 (0)1223 420257
> >
> >
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