cayenne-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Ricardo Parada <rpar...@mac.com>
Subject Re: Expression to look for objects with an empty to-many relationship?
Date Sat, 25 Jul 2015 23:39:11 GMT
On the EOF/Wonder world we have ERXExistsQualifier. I don't know how different cayenne is but
it might be worth looking at it and try to mimic it. 

For example, if you have a Family entity. a Pet entity and a pets to-many relationship from
family to Pet then you would be able to build qualifiers than answer questions like these:

Get families with pets
Get families with zero pets
Get families with puppies (where puppies is a sub qualifier on the Pet entity)
Etc...

The qualifiers work in memory or database equally well. 

> On Jul 24, 2015, at 12:56 PM, Hugi Thordarson <hugi@karlmenn.is> wrote:
> 
> Indeed :). I’ve been looking at the Expression classes for a while now and they look
a little daunting. Any recommendations on where to start? Is there a developer guide or an
annotated example implementation somewhere?
> 
> - hugi
> 
> 
> 
>> On 24. júl. 2015, at 15:59, Andrus Adamchik <andrus@objectstyle.org> wrote:
>> 
>> Classic open source - "scratch your own itch" :) 
>> 
>> 
>>> On Jul 24, 2015, at 6:54 PM, Hugi Thordarson <hugi@karlmenn.is> wrote:
>>> 
>>> Thanks Andrus, we’ll revert to EJBQL for now.
>>> 
>>> Looks like an excellent opportunity to try and implement my first Expression
class :)
>>> 
>>> - hugi
>>> 
>>> 
>>> 
>>>> On 24. júl. 2015, at 15:36, Andrus Adamchik <andrus@objectstyle.org>
wrote:
>>>> 
>>>> We should add it. For now OUTER JOIN should do the trick:
>>>> 
>>>> "a.paintingArray+ = null"
>>>> 
>>>> Also EJBQL syntax supports "IS [NOT] EMPTY" :
>>>> 
>>>> "SELECT a FROM Artist a WHERE a.paintingArray IS EMPTY"
>>>> 
>>>> Andrus
>>>> 
>>>>> On Jul 24, 2015, at 5:51 PM, Hugi Thordarson <hugi@karlmenn.is>
wrote:
>>>>> 
>>>>> Hi all.
>>>>> Does Cayenne have an Expression class that allows searching for objects
with an empty to-many relationships? If not, any pointers towards a sensible approach?
>>>>> 
>>>>> Cheers,
>>>>> - hugi
>>>>> 
>>>>> // Hugi Thordarson
>>>>> // http://www.loftfar.is/ <http://www.loftfar.is/>
>>>>> // s. 895-6688
> 

Mime
View raw message