Re: [eclipselink-users] Conditional LEFT JOIN in JPQL

[Tom Ware <tom.ware@xxxxxxxxxx>]

1. Constructors are supported through ReportQuery.  See 
ReportQuery.addConstructorReportItem(ConstructorReportItem item).  There should 
be nothing different about using these with a query key

2. Parameters are available in your query, but not in the query key you are 
using for your ON clause.  The issue of Parameters in the ON Clause should be 
addressed as part of the solution when bug 312146 is addressed.  I suspect that 
to fix this issue, we would add explicit "ON" API rather than expanding how 
QueryKeys work.

3. Named queries can be added in a SessionCustomizer.  See 
Session.addQuery(name, databaseQuery).  Any query added to the session will be 
available through the Named Query API. Here is some information about customizers.

http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29#Using_EclipseLink_JPA_Extensions_for_Customization_and_Optimization
http://wiki.eclipse.org/Introduction_to_EclipseLink_Sessions_%28ELUG%29#Session_Customization
http://wiki.eclipse.org/Introduction_to_Descriptors_%28ELUG%29#Descriptor_Customization

-Tom

bht@xxxxxxxxxxxxx wrote:
> Hi Tom,
>
> I have a few questions regarding
> https://bugs.eclipse.org/bugs/show_bug.cgi?id=312146
>
> 1) Can I use a DTO constructor in the EL API query such as in the
> attached tescase: select new dto.ProductWithFavoriteDTO(p, f) from
> Product left join p.favorites f
>
> 2) Can I pass a parameter userId into such a query. If not, is
> https://bugs.eclipse.org/bugs/show_bug.cgi?id=312146 addressing this?
>
> I need this behavior because the query is expensive. Please refer to
> 3).
>
> 3) How can I manipulate this query in such a way that it is cached in
> EntityManager across sessions, much like a @NamedQuery with
> parameters?
>
> Tom, thanks again for your help. I don't want to sound too demanding,
> but as a suggestion my questions could be addressed in an easy way by
> extending the testcase attached to
> https://bugs.eclipse.org/bugs/show_bug.cgi?id=312146
>
> This might be useful for other people too, and it could be posted as
> an example (being as simple as it is), and in case of future questions
> one could just link to it.
>
> Many thanks,
>
> Bernard
>
>
>
> On Tue, 11 May 2010 08:20:05 -0400, you wrote:
>
> > Hi Bernard, Vidas,
> >
> >   The best way to get this feature to the top of our implementation list is to 
> > vote for it.  One of the main criteria we use when determining which features to 
> > implement next is the number of distinct votes.
> >
> >   I have updated the bug with some information about how to define a query that 
> > retrieves multiple items.
> >
> >   If you want to dynamically define a QueryKey, I believe it should work at the 
> > moment.  You will have to use a small amount in internal API.  Here is some 
> > pseudo code for the basic steps.
> >
> >   ServerSession session = 
> > (ServerSession)JpaHelper.getServerSession(myEntityManagerFactory)
> >   ClassDescriptor descriptor = session.getDescriptor(MyEntity.class);
> >   descriptor.addQueryKey(myQueryKey);
> >   myQueryKey.initialize(descriptor);
> >
> >   The changes that allow JPQL queries to use query keys will be in our 2.1 
> > release.  They appear in our nightly builds starting with last night's build.
> >
> > -Tom
> >
> > Vidas Timukas wrote:
> > > Hi, Bernard,
> > >
> > >   Know nothing about EL API, but, according to Tom's example, might it 
> > > be possible to define queryKey on the fly with User.getId() as 
> > > ConstantExpression and destroy it after query execution. Maybe Tom can 
> > > suggest something about this.
> > >   Another question, which rises, how to retrieve both objects in result 
> > > list, like List<Product, Favourite>, because ReadAllQuery(Product.class) 
> > > from given example seems to return only list of Products.
> > >   And last question for Tom: As you said, there is some work to support 
> > > queryKeys in JPQL. Can you tell us, in which version of EL it will be 
> > > supported:? For example:
> > >
> > >   SELECT p, f FROM Product p join p.favouritepk f 
> > >
> > >
> > >
> > > 2010/5/11 <bht@xxxxxxxxxxxxx <mailto:bht@xxxxxxxxxxxxx>>
> > >
> > >     Hello Vidas,
> > >
> > >     I created a testcase and Tom responded to it:
> > >
> > >     https://bugs.eclipse.org/bugs/show_bug.cgi?id=312146
> > >
> > >
> > >     Can you believe that even with the current EclipseLink version, using
> > >     the proprietary EclipseLink API, it is not possible to write a query
> > >     with a conditional join where the condition comes from a parameter
> > >     value?
> > >
> > >     This is the simplest case I have been able to suggest. So no userId
> > >     parameter for the query :(.
> > >
> > >     It looks like I have to wait for some time (months?, a year?) before
> > >     this is implemented, even before the spec is changed.
> > >
> > >     Would you have any comment? Please vote for this.
> > >
> > >     Best regards,
> > >
> > >     Bernard
> > >
> > >     _______________________________________________
> > >     eclipselink-users mailing list
> > >     eclipselink-users@xxxxxxxxxxx <mailto:eclipselink-users@xxxxxxxxxxx>
> > >     https://dev.eclipse.org/mailman/listinfo/eclipselink-users
> > >
> > >
> > >
> > >
> > > --
> > > Sincerely,
> > > Vidas
> > >
> > >
> > > ------------------------------------------------------------------------
> > >
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