Re: possible to write a JPA Query to that filters both an Entity and its relationship entities?

[Craig L Russell]

Hi Patrick,

From the JPQL



I expect to get SQL that looks something like






Craig

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

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

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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
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:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!

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

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