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Subject: AW: Joins and performance
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Date: Fri, 1 Jun 2007 15:39:32 +0200
Message-ID: <5EE5137D79A3CA45970354F512B3F3E3B4DFF8@m-ex1.gt.local>
Thread-Topic: Joins and performance
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From: "Vitzethum, Daniel" <Daniel.Vitzethum@gigatronik.com>
To: "Apache Torque Users List" <torque-user@db.apache.org>

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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