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From Andrus Adamchik <>
Subject Re: Cayenne and Spring (a Hibernate inspired question)
Date Thu, 28 Feb 2008 12:56:07 GMT
3.0 EJBQLQuery should be able to handle that.


On Feb 28, 2008, at 2:44 PM, Marcin Skladaniec wrote:

> Hi
> Short comment on the cayenne sorted queries, they work great but be  
> aware of a limitation:
> (the query examples assume one to many relation Artist-Painting)
> SelectQuery query = new SelectQuery(Painting.class);
> query.addOrdering(Painting.ARTIST_PROPERTY+"."+Artist.LAST_NAME,true);
> will not return the Paintings without artist. This behaviour is  
> correct 90% of the times, but would be awesome if it could be  
> controlled and customized so the null in the order path does not  
> alter the results.
> also be aware that a query for a relationship existence (or non- 
> existence) does not work:
> SelectQuery query = new SelectQuery(Painting.class,  
> ExpressionFactory.matchExp(Painting.ARTIST_PROPERTY, null));
> so you might need a flag to indicate whether the relationship is set  
> or not to allow easy querying and/or sorting.
> If someone has a (simple) workaround to the problems I mentioned  
> please share!
> Cheers
> Marcin
> On 29/02/2008, at 8:03 AM, Marek Wawrzyczny wrote:
>> Thanks Kevin,
>> Your response was quite encouraging. Most of the pages are very  
>> simple but
>> there is one or two which enforces quite coplex workflow. It's a  
>> perfect
>> candidate for a child context.
>> Just out of curiosity, how do people manage contexts in a typical  
>> application containing several (>10) entities. We're also using   
>> AJAX calls
>> (DWR).
>> Regarding queries. Hibernate often handles lazy initialized  
>> relationships very
>> badly. There are two bugs I've hit where both HSQL and the Criteria  
>> API (kind
>> of like the query builder API in Cayenne) have trouble creating the  
>> SQL
>> query. Take the following two entities:
>> Course
>> name
>> classes
>> Cllass
>> course
>> startsOn
>> endsOn
>> Hibernate could potentially have trouble building a query that  
>> would return
>> courses where we discrimante on both startsOn and endsOn properties  
>> of a
>> Class.
>> An additional bug may prevent ordering on either startsOn or  
>> endsOn  if the
>> property was used in the query.
>> The issue is with the way Hibernate aliases the joins in the  
>> resultset.
>> Obviously, I'd want to avoid that in the future.
>> Cheers,
>> Marek Wawrzyczny
>> On Thu, 28 Feb 2008 00:51:59 Kevin Menard wrote:
>>> Hi Marek,
>>> My Hibernate experience is limited to a single project that did  
>>> not use
>>> Spring, so it's hard for me to draw a fair comparison.  My take from
>>> passively watching on discussion lists (particularly the Tapestry  
>>> one)
>>> is that Spring makes Hibernate usable in a way that Cayenne is out  
>>> of
>>> the box.  It seems you know this already, though.
>>> In a Web app I have here, we an account creation operation split  
>>> up over
>>> three screens and it involves several different entities.  For  
>>> this, I
>>> simply used a peer context per page and coalesce everything at the  
>>> end.
>>> This is a little bit older code and I would likely use a child  
>>> context
>>> for it now.  The reason I did it this way is that while  
>>> conceptually a
>>> single operation, completing any of the phases is a complete
>>> transaction.  If you want to enforce start to finish behavior, you  
>>> could
>>> use a single context shared via session.  Just watch yourself  
>>> because
>>> it's a lot harder to enforce a workflow through a browser than it is
>>> through Swing.
>>> As for sorting across multiple relationships, I guess I would have  
>>> to
>>> understand a little more as to what you want to do.  Simplest  
>>> thing is
>>> to write your own Comparator, but you may want to look at mapping a
>>> query, and barring that, use SQLTemplate to achieve what you need  
>>> in the
>>> DB.
>>> I hope that helps.

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