I think that Tom is looking for a way to get back just those employees
that are > 15 years, so that he could display something like so:
Department: R&D
Old-timers: Larry, Curly, Moe
Department: Entertainment
Old-timers: Fred, Ginger
IOW, he's not looking for departments that have old-timers, but rather
looking for the departments with old-timers and *just* the old-time
employees.
I think that Dain's suggestion of turning it around, plus appropriate
ordering, is the best bet:
select e from Employee e where e.tenure >= 15 order by e.dept
This will require some post-processing to turn the single ordered list
into a list of lists, but you could probably do that inline with the
display logic if performance becomes a concern.
OpenJPA can definitely be tuned (using the Query's FetchPlan) to eagerly
join the emp=>dept relation:
OpenJPAQuery q = OpenJPAPersistence.cast(em.createQuery(
"select e from Employee e where e.tenure >= 15 order by e.dept"));
q.getFetchPlan().addField(Employee.class, "dept");
List<Employee> emps = (List<Employee>) q.getResultList();
-Patrick
--
Patrick Linskey
BEA Systems, Inc.
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> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
> Sent: Thursday, February 22, 2007 3:41 PM
> To: open-jpa-dev@incubator.apache.org
> Subject: Re: possible to write a JPA Query to that filters
> both an Entity and its relationship entities?
>
> What about something like:
>
> select distinct e.department from employee e where
> e.department.deptno
> >=100 and e.yearsOfService>=15
>
>
> Not sure if the above will do the trick without trying it myself...
>
> Dain Sundstrom wrote:
> > I'm no JPA expert, so take my comments with a grain of salt.
> >
> > How about searching the other direction:
> >
> > select e from employee e where e.department.depno >= 100 &&
> > e.yearsOfService >= 15
> >
> > Then assuming OpenJPA can do it, you could tune the query
> to grab the
> > department object along with the employee. If OpenJPA
> can't do that,
> > you will get at most 100+1 queries. Alternatively, you could try
> > executing this query before the one above:
> >
> > select d from Department d WHERE d.deptno >= 100
> >
> > And then rely on the OpenJPA cache to hook the departments to the
> > employees. Depending on the database vendor and the data in the
> > tables, executing two queries may be more efficient then one.
> >
> > -dain
> >
> > On Feb 22, 2007, at 12:21 PM, Tom Mutdosch wrote:
> >
> >> Hi there,
> >> I have a question about JPA Queries containing relationships and a
> >> WHERE filter. I basically want to have a JSF page containing a
> >> datatable that shows a list of Departments - each Department row
> >> shows relevant columns (department name, ID, etc) as well
> as a nested
> >> list of that Department's Employees with 15 or more years
> of service.
> >> I was wondering if there was any way to create a JPA query
> that would
> >> return me such a result using just a single query. From
> what I have
> >> heard, I don't believe this is possible but thought I'd
> ask here just
> >> to be sure. As far as I know, JPA will just return me the
> >> Departments that match that query and each Department will contain
> >> every Employee that belongs to it.
> >>
> >> Background: I have a DEPARTMENT entity with a one-to-many
> >> relationship to an EMPLOYEE entity. On my web page, I want to
> >> display "departments with a department number >= 100 and
> containing
> >> EMPLOYEES with more than 15 years of service".
> >>
> >> Using SDOs I was able to write a query that would return a List of
> >> results which I would then bind to my JSF datatable. This
> list would
> >> contain Departments, and the Departments would have the Employees
> >> that matched that criteria. To do something similar in
> JPA, I think
> >> I now need to do n + 1 queries. That is, one query to
> retrieve the
> >> departments that I want to display, and then for each department
> >> another query to get the filtered list of its Employees.
> >> In summary, I basically want to do something like:
> >> select d from Department d LEFT JOIN d.employeeCollection e WHERE
> >> d.deptno >= 100 AND e.yearsOfService >= 15
> >>
> >> But I think I need to do two separate queries. One to get the
> >> departments:
> >> select d from Department d WHERE d.deptno >= 100
> >>
> >> Then for each Department returned in that result set, a separate
> >> query to get the employees I'm after:
> >> select e from Employee e where e.department.deptno = d.deptno and
> >> e.yearsOfService >= 15
> >>
> >>
> >> Does this sound like the right/only way to do this?
> >> Thanks,
> >> Tom
> >>
> >>
> >>
> >>
> >
>
