[rules-users] ClassCastException and other problems

[Sibylle Duerr]

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