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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 Sat, 24 Feb 2007 00:13:56 GMT
Hi Patrick,

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

I expect to get SQL that looks something like
select dept.id, dept.name, oldtimers.id, oldtimers.firstname,  
oldtimers.lastname, oldtimers.salary, oldtimers.ssn from Department  
dept, Employee oldtimers WHERE dept.id = oldtimers.deptid AND  
dept.deptno >= 100 AND  oldtimers.yearsOfService >= 15

I then construct instances from the returned dept and oldtimers  
columns and give back to the user the results, with one result row  
for each SQL ResultSet row. So the filtering from the JPQL translated  
into the WHERE clause in the SQL should exclude oldtimers that don't  
qualify.

If you don't use the oldtimers.yearsOfService >= 15 in the SQL, then  
you will get all of the employees in the department returned in the  
result. But why do you not use the oldtimers.yearsOfService >= 15 in  
the SQL?

Craig

On Feb 23, 2007, at 2:12 PM, Patrick Linskey wrote:

>> In fact, you have to do a bit of work to get SQL to return you non-
>> filtered instances. So I don't get it. Does OpenJPA not
>> construct the
>> obvious SQL that filters oldtimers?
>
> I don't think that you and I are really in sync here. Maybe some more
> concrete examples are in order?
>
> -Patrick
>
> -- 
> Patrick Linskey
> BEA Systems, Inc.
>
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>> -----Original Message-----
>> From: Craig.Russell@Sun.COM [mailto:Craig.Russell@Sun.COM]
>> Sent: Friday, February 23, 2007 2:09 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?
>>
>> So,
>>
>> I can tell you that having a result column that is filtered in the
>> query is not what a user would expect. In JDO, the oldtimers column
>> would be filtered.
>>
>> In fact, you have to do a bit of work to get SQL to return you non-
>> filtered instances. So I don't get it. Does OpenJPA not
>> construct the
>> obvious SQL that filters oldtimers?
>>
>> I've re-read the JPA specification, and it appears to be silent on
>> the issue of filtering. Is this a portability issue?
>>
>> Craig
>>
>> On Feb 23, 2007, at 1:57 PM, Tom Mutdosch wrote:
>>
>>> Hi Patrick,
>>> Thanks for the query suggestion.  I guess what I was initially
>>> thinking of doing was incorrect in that JPA doesn't really give me
>>> a "view" of what I want.  That is, I can never get a Department
>>> object containing a list of filtered Employees.  A JPA object
>>> returned from a query is always going to be an exact
>> representation
>>> of the database.  So your Department object is always going to
>>> contain all of the Employees in its relationship.
>>>
>>> So like you mentioned, I can still get all the information using
>>> one query, and then just process those results as I want them.  I
>>> imagine that this would entail some sort of wrapper bean
>> that would
>>> house the Department and the filtered list of Employees.  Or what
>>> if I added a regular method to my Department entity called
>>> getFilterEmployees() which would return a List that I populated
>>> with the filtered results from my query?  Does that seem like a
>>> reasonable thing to do -- if I didn't want to deal with a wrapper
>>> object but still have all of my desired data captured by a single
>>> Entity?
>>> Thanks
>>> Tom
>>>
>>>
>>> Patrick Linskey wrote:
>>>> It is, but it doesn't buy you much in this situation --
>> the oldTimers
>>>> collection in your example won't be filtered to just the
>> ones that
>>>> are
>>>> old. It'll be all the employees in the dept.
>>>>
>>>> -Patrick
>>>>
>>>>
>>
>> Craig Russell
>> Architect, Sun Java Enterprise System http://java.sun.com/products/ 
>> jdo
>> 408 276-5638 mailto:Craig.Russell@sun.com
>> P.S. A good JDO? O, Gasp!
>>
>>

Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:Craig.Russell@sun.com
P.S. A good JDO? O, Gasp!


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