I'm sorry, I didn't mean what I said about you, I had bad day,
shouldn't write that email :/
Please, do not take it personally.
2007/6/23, Witold Szczerba <pljosh.mail_at_gmail.com>:
> 2007/6/23, glassfish_at_javadesktop.org <glassfish_at_javadesktop.org>:
> > Well, I won't comment on how horrible the whole statement is, because I'm confident that it's an example to prove a point rather an idiom you're practicing in code.
> > Everyone knows for large queries like that you should be selecting as much as you
> > can in a single network hit through joins rather than making a gazillion
> > network hits. Common sense.
>
> THE statement was only to show the problem, it is the real statement we do use.
> You must be really out of any reality to say what you said. The
> em.getReference SHOULD NOT produce any query, as it is only to provide
> some kind of >stub< (for example for use in query.setParameter(xxx,
> em.getReference(SomeClass.class, someID);
>
> Many times, it is necessary to provide only a REFERENCE to an object,
> which is what em.getReference should provide, without actually
> fetching anything from database.
>
> > For example:
> > [code]
> > Query q = em.createQuery("SELECT l FROM Loan l");
> > for (Loan l : q.getResultList()) {
> > ....
> > }
> > [/code]
> > will run in a heartbeat compared to what you posted.
>
> NO, because I am REALLY not interested in fetching 70 thousand loans in a query.
>
> > If the object by the primary key is within either the level 1 or level 2 cache, find will NOT hit the DB.
>
> Consider this: I am not really interested in fetching given loan at all...
>
> > Anyway, bottom line, the EM is doing everything properly. It's a feature, not a bug.
>
> As long as it is really trying to fetch all the data for loans I am
> not really interested in, I am not happy. With plain SQL I can get
> LoanID using only one single "long" and that is really enough to
> provide a foreign key to any other statement. Current em.getReference
> is invoking 4 or 5 huge queries into database, only to give me the ID
> which is the only thing I need.
>
> >I consider the example you posted bad form for any data set of reasonable size.
>
> As I said, you have probably never had to write any complex
> application with JPA QL. Anything other than just a simple tutorial
> will show you the need for getting a _reference_ to entities.
>