You might also want to follow the Java Data Objects (JDO)
spec at Sun. I recently attended a seminar at the Silicon
Valley Java Users Group where a rep from Versant was discussing
this. It sounds very similar to what you are mentioning below.
>From: Alexandre Lefebvre <[EMAIL PROTECTED]>
>Reply-To: [EMAIL PROTECTED]
>To: "'[EMAIL PROTECTED]'"
><[EMAIL PROTECTED]>
>Subject: Re: Question re: CMP, JEntityHome, JBeanEntity implementation
>Date: Fri, 05 May 2000 10:15:52 +0000
>
>Yes, the current version of JOnAS is not optimized.
>
>The first query, which corresponds to the findByPrimaryKey, is about
>verifying that the identifiers (PK) are valid.
>The second query is issued when a business method is called, in order for
>the container to load the objet attributes into main memory.
>
>France Telecom R&D is currently working on an adaptable persistence layer
>for Java objects called JORM (Java Object Repository Mapping).
>JORM will be integrated in a future version of JOnAS, in order to provide
>enhanced CMP (including persistent inter-bean references and polymorphism
>of entity beans).
>
>The plan is then to develop a caching mechanism (see also Adam McClure's
>reply to this message) on top of JOnAS + JORM. This cache would indeed
>limit the waste of resources.
>
> alex
>
>Bryan Field-Elliot wrote:
>
> > We use CMP beans extensively, and I am examing the code generated by
>GenIC
> > for "JOnAS###Bean###Home" and "JOnAS###Bean###" (where ### is the name
>of my
> > bean). This is the code which implements the JEntityHome and JBeanEntity
> > interfaces.
> >
> > It seems that _two_ queries get issued for every finder method, but it
>seems
> > to me that the job can be done with only one. This is a big performance
> > problem for us, and would be a great performance boost if we could make
>it
> > into one query.
> >
> > For example, if I have a table called "Employees" with a primary key
>"id"
> > and other fields "name" and "job", then a findByPrimaryKey(100) would
>result
> > in the following two queries:
> >
> > select Employees.id from Employees where Employees.id=?
> > select Employees.id, Employees.name, Employees.job from Employees where
> > Employees.id=?
> >
> > The first is issued by the Home interface implementation
> > (pkFindByPrimaryKey), and the second is implemented by the Bean
> > implementation (loadData).
> >
> > As far as I can see, the first query is a big waste of resources, and
>pretty
> > much cuts performance in half. I don't understand why the first query is
> > executed at all, since it's function (to check whether or not the row
> > exists) can be performed by the second query just as well.
> >
> > Can someone please explain why it works this way, and if possible, how
>to
> > optimize it?
> >
> > Thank you,
> > Bryan
> >
> >
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