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 $models
Simply does not match, instead of raises a CCE, in case the model is a TypeModel.
But for 4.0.x, that is how things work.
The only suggestion I can give you is, in your second problem, to not return null on your collections. Simply return empty collections:
class Project {
...
public List getModels() {
if( this.models == null ) {
return Collections.emptyList();
}
return this.models;
}
...
}
This is usually a good thing, unless you have a specific semantics for null collections in your domain model.
[]s
Edson
2008/6/6 Sibylle Duerr <sibylle.duerr@mymail.ch>:
Hi there,
I have three issues, where I'm not sure if these are bugs in
drools, or if this is just the way it has to be.
the used classes in this case are:
Project
Model
ProcessModel extends Model
only the Project is in the working memory, because I didn't want
to load all elements due to performance issues (there can be
thousends of elements to load at startup).
if I have the following rule:
Project($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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