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From "Greg Monroe" <Greg.Mon...@DukeCE.com>
Subject RE: Joins and performance
Date Fri, 01 Jun 2007 14:14:52 GMT
If this is a frequent/heavily used query, another way to deal with 
this is to create a view and a matching Torque object.  There is 
a table option that suppresses the SQL generation.  You can then
just use the Peer/Record object as like it was a normal table.

Note you may want to pay close attention to the indices requirements
of the underlying table.  If commonly used columns in a large join
are not index, it can be a BIG performance hit.

> -----Original Message-----
> From: Vitzethum, Daniel [mailto:Daniel.Vitzethum@gigatronik.com] 
> Sent: Friday, June 01, 2007 9:40 AM
> 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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