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From Craig L Russell <Craig.Russ...@Sun.COM>
Subject Re: possible to write a JPA Query to that filters both an Entity and its relationship entities?
Date Fri, 23 Feb 2007 00:54:50 GMT
How about

select dept, oldtimers from Department dept LEFT JOIN  
dept.employeeCollection oldtimers WHERE dept.deptno >= 100 AND   
oldtimers.yearsOfService >= 15

That should give you only departments that satisfy the deptno  
constraint and since you are not using outer join, only departments  
that also have at least one employee satisfying the yearsOfService  

The results would have one element for each employee. Each result row  
would contain the department and the employee. So you would have the  
[looks better in monospace font]
dept            oldtimers
=============   ==============
R&D             Larry
R&D             Curly
R&D             Moe
Entertainment   Fred
Entertainment   Ginger


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

Craig Russell
Architect, Sun Java Enterprise System
408 276-5638
P.S. A good JDO? O, Gasp!

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