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From Andrus Adamchik <and...@objectstyle.org>
Subject Re: Referencing ID fields in EJBQL
Date Fri, 04 Dec 2009 08:39:06 GMT
Yeah, in 3.0 EJBQL is somewhat of an implant from the JPA world, so it  
lacks a few Cayenne conveniences. I am certainly in favor to add  
support for "db:" expressions in the future versions (and the patches  
are welcomed).

For now the option is to map PK column as the object property. Other  
than exposing it to the world, this shouldn't have any side effects.  
Auto generation will still work, etc.

Andrus

On Dec 4, 2009, at 12:05 AM, Dave Lamy wrote:

> Hello all--
>
> I am curious to know how (if possible) to reference a PK field using  
> EJBQL.
>
> I tried using the normal expression "db:" syntax but as I saw in the  
> source
> this won't work.  EJBQLPathTranslator.processLastPathComponent()  
> appears to
> assume that the last part of any path will reference either an  
> ObjAttribute
> or an ObjRelationship, and will throw an IllegalStateException if  
> neither of
> these are the case.
>
> I'd like to have access to the PK field for a couple of purposes.   
> One, when
> doing COUNT queries it is faster to do a COUNT(PK) than a COUNT(*).
> Furthermore, I want to be able to essentially group aggregate function
> results by objects, which would be impractical to do using the  
> OBJECT(e)
> notation, so the plan was to perform the group query using IDs and  
> then fill
> in the results with objects on the way out.
>
> Since the call from processLastPathComponent() to
> processTerminatingAttribute() just resolves into a DbAttribute and  
> thus a
> column name anyway, wouldn't it be rather simple patch to do a "db:"  
> check
> on the path component and presume a DB column name instead of an
> ObjAttribute name?  I imagine I may be oversimplifying the  
> situation, but if
> not and there is agreement on the method I don't mind doing the patch.
>
> Of course, if there is an alternative way to reference PKs that I'm  
> unaware
> of please enlighten me :-).
>
> Thanks--
> Dave


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