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From "Robert Kromkamp" <r.kromk...@pagelink.nl>
Subject RE: Joins and performance
Date Fri, 01 Jun 2007 14:26:13 GMT
Hi Daniel,

That's exactly what I was looking for!!!!

Thanks for your reply! This is very usefull.

I found the discussion about the class you mentioned below. It's in:

http://www.mail-archive.com/torque-user@db.apache.org/msg03571.html


But I've the feeling this could be an old version casue still
Peer.doSelect is used instead of Peer.doSelectVillageRecords(). Is this
correct? Can you tell me where to find the newest version or perhaps
could you send it to me?

In some cases I use LargeSelect (with paging). Do have a same kind of
solution for handle such kind of queries?

Thanks,
Robert

-----Original Message-----
From: Vitzethum, Daniel [mailto:Daniel.Vitzethum@gigatronik.com] 
Sent: Friday, June 01, 2007 3:40 PM
To: Apache Torque Users List
Subject: AW: Joins and performance

Hi Robert,

> If I've 100 companies (which are schools) and 200 buildings, I will 
> executes 100 * 200 queries to get all the employees.

be sure to avoid this... sounds like a killer ;-)

> In low level SQL
> this query can be combined in one query. Is there a way to handle this

> within Torque?

In Torque, you can use the Criteria.addJoin() method to link two tables.


Using that feature, you cannot use the Peer.doSelect() method, but have
to use Peer.doSelectVillageRecords(), which will return all columns of
all joined tables in a village Record object, with no big difference to
plain JDBC in handling. If you need or want Torque data objects, you
have to extract them one by one from the result set.

For a project of us, we wrote a helper class named JoinHelper that does
this business for you AND returns an tree of Torque objects. In your
case, it would return COMPANY objects that can be queried for their
BUILDINGs, which again know their EMPLOYEEs.

Please search the thread about two years ago in Torque archive and the
discussion about. JoinHelper massively uses reflection, but is tested
quite well and in production. If you have more detailled questions...
you're welcome.


Daniel

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