[rules-users] ClassCastException and other problems

[Sibylle Duerr]

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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>
>
>
> -- 
> 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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