Thanks a lot Andrus! I’m going to play around a little with this and see if I
can’t make something useful of it :)
Cheers,
- hugi
> On 27. júl. 2015, at 08:49, Andrus Adamchik <and...@objectstyle.org> wrote:
>
> In the most general case adding support for a new kind of expression requires
> the following:
>
> 1. Support in ExpressionFactory and Property classes (though see comment
> below on CollectionProperty)
> 2. Support in Expression parser (so that the expression can be created from
> String)
> 3. Support in SelectTranslator (so that the expression can be converted into
> SQL).
>
> In your case a minimal implementation can be quite simple: implement #1 to
> work as outer join example ("a.paintingArray+ = null"). So existing #2 and #3
> will be reused. Perhaps we create a Property subclass for to-many
> relationships (CollectionProperty or something) that will have that extra
> method for empty. Then you will also need to tweak cgen templates so that
> CollectionProperty is included in generated classes.
>
> Next step may be adding EJBQL syntax to Expression parser (#2): path IS [NOT]
> EMPTY
>
> And finally we may decide to generate SQL different from OUTER JOIN (EXISTS,
> etc.). Only here this expression becomes truly "new". If you get to this
> step, let's discuss it separately on this list. We will need to discuss the
> behavior and SQL we should generate. Also Alex Kolonitsky is now working on a
> new SelectTranslator to include aggregates, etc., so this step will likely
> overlap with his work.
>
> Andrus
>
>
>> On Jul 24, 2015, at 7:56 PM, Hugi Thordarson <h...@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 <and...@objectstyle.org> wrote:
>>>
>>> Classic open source - "scratch your own itch" :)
>>>
>>>
>>>> On Jul 24, 2015, at 6:54 PM, Hugi Thordarson <h...@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 <and...@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 <h...@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
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
