[rules-users] ClassCastException and other problems

[Edson Tirelli]

      Drools 5 implements a completely new propagation algorithm that
allowed us to get rid of shadow proxies from the core engine. So, you will
not have the problem.

      But for 4.0.x, if you are a community user, best you can do is open a
JIRA with a test case to reproduce your problem. If we release a 4.0.8
version, we can fix your issue there, but at this moment we don't know if
there will be a 4.0.8 release or if the next release will be 5.0.
      If you are a Drools subscriber at Red Hat, then you can simply open a
support case there and they will fix and provide a patch for you.

      []s
      Edson



2008/6/6 Sibylle Duerr <sibylle.duerr at mymail.ch>:

> Thanks Edson,
>
> but the collections do return an empty collection. hm, I just tested this
> ones again and it worked fine. no exception when the set was empty. I will
> keep an eye on this and test some more but seems to work now for me.
>
> and for the other problem I then hope for 5.0 :).
>
> and what about the last problem I described before?
>
> best regards
> Sibylle
>
>
>
> Edson Tirelli wrote:
>
>>
>>
>>   Sibylle,
>>
>>   Unfortunately, this is the way it was implemented to be, under a kind-of
>> "fail-fast" philosophy we were following. I do think there is value in
>> changing things in 5.0 so that, for instance:
>>
>> ProcessModel($activities : activities) from $models
>>
>>   Simply does not match, instead of raises a CCE, in case the model is a
>> TypeModel.
>>   But for 4.0.x, that is how things work.
>>
>>    The only suggestion I can give you is, in your second problem, to not
>> return null on your collections. Simply return empty collections:
>>
>> class Project {
>>   ...
>>   public List getModels() {
>>        if( this.models == null ) {
>>            return Collections.emptyList();
>>        }
>>        return this.models;
>>   }
>>   ...
>> }
>>     This is usually a good thing, unless you have a specific semantics for
>> null collections in your domain model.
>>
>>    []s
>>    Edson
>>
>> 2008/6/6 Sibylle Duerr <sibylle.duerr at mymail.ch>:
>>
>>    Hi there,
>>
>>    I have three issues, where I'm not sure if these are bugs in
>>    drools, or if this is just the way it has to be.
>>
>>    the used classes in this case are:
>>
>>    Project
>>    Model
>>    ProcessModel extends Model
>>
>>    only the Project is in the working memory, because I didn't want
>>    to load all elements due to performance issues (there can be
>>    thousends of elements to load at startup).
>>
>>    if I have the following rule:
>>
>>    Project($models : models)
>>    ProcessModel($activities : activities) from $models
>>
>>    there happen to be two problems. if the project does not only
>>    contain ProcessModels but also TypeModels or others (all extend
>>    Model), this leads to a ClassCastException.
>>    I can solve this by writing the rule as follows:
>>
>>    Project($models : models)
>>    $m : Model(eval($m instanceof ProcessModel)) from $models
>>    ProcessModel($activities : activities) from $m
>>
>>    but this is not really nice and I hope there is a better solution
>>    for this, is there?
>>
>>    the second problem this rule gives me, is when the set 'models' is
>>    empty. that will also throw an exception. to solve this I write:
>>
>>    $p : Project(eval($p.hasModels()), $models : models)
>>    $m : Model(eval($m instanceof ProcessModel)) from $models
>>    ProcessModel($activities : activities) from $m
>>
>>    and I need to use this in each case where I have possible empty sets.
>>
>>
>>    the last problem I encountered when I tried to load all elements
>>    to the working memory and then redefine some rules. used classes:
>>
>>    Aggregation extends DomainElement
>>
>>    rule:
>>
>>    Aggregation(owner.owner != type.owner)
>>
>>    causes some exception. the root exception is a ClassCastException:
>>    ProxyShadowProxy cannot be cast to Aggregation.
>>    when I rewrite the rule as:
>>
>>    $element : DomainElement(eval($element instanceof Aggregation))
>>    Aggregation(owner.owner != type.owner) from $element
>>
>>    everything works fine. but that again is not a nice solution.
>>
>>    any help?
>>
>>    best regards
>>    sibylle
>>    _______________________________________________
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>>    https://lists.jboss.org/mailman/listinfo/rules-users
>>
>>
>>
>>
>> --
>> Edson Tirelli
>> JBoss Drools Core Development
>> Office: +55 11 3529-6000
>> Mobile: +55 11 9287-5646
>> JBoss, a division of Red Hat @ www.jboss.com <http://www.jboss.com>
>> ------------------------------------------------------------------------
>>
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-- 
Edson Tirelli
JBoss Drools Core Development
Office: +55 11 3529-6000
Mobile: +55 11 9287-5646
JBoss, a division of Red Hat @ www.jboss.com
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