Re: [rules-users] ClassCastException due to binding
"Polymorphic bindings" are not supported, the fact that it's not
reported at compilation time,
but only throws an exception at runtime, is a bad bug (I'll open a ticket)
This said, you can split your rule in two rules - which is what Drools
would do anyway:
rule r1 when $x : Foo() then .. end
rule r2 when $x : Bar() then .. end
I'd also encourage you to follow java conventions, using capital letters
for declared types.
And there may be various alternatives to "describe why a rule fired",
both in and out the RHS of a rule.
To cite some, using AgendaEventListeners or "drools.getActivation()" in
the RHS.
Davide
On 06/04/2013 05:12 PM, bdolbeare wrote:
We have a need to support binds for conditional or elements so that
we can
describe why a rule fired in the then clause of a rule. The following DRL
is a simple example of what we are trying to do. There are two versions of
our rule in the DRL:
*rule "WORKING: find with or"*: works but only because the first variable
we try to bind in the or expression is of type "target" which is a super
class of the other elements in the or expression.
*rule "BROKEN: find with or"*: causes a class cast exception when the
"bar" pattern is matched because the then clause tries to store the bar
object in handle "x" which it thinks is of type "foo".
Is there a way to define the object type for the bind variable?
Is there any other way to make something like this work?
package tests
import org.apache.log4j.Logger;
global Logger log
declare target
notreal : boolean
end
declare foo extends target
foovalue : String
end
declare bar extends target
barvalue : String
end
rule "insertdata"
when
then
insert(new foo(false, "a"));
insert(new bar(false, "b"));
end
rule "WORKING: find with or"
when
( or x: target(notreal)
x: foo(foovalue == "a")
x: bar(barvalue == "b")
)
then
log.info("i found object: " + x);
end
rule "BROKEN: find with or"
when
( or
x: foo(foovalue == "a")
x: bar(barvalue == "b")
)
then
log.info("i found object: " + x);
end
Exception executing consequence for rule "find with or" in tests:
java.lang.ClassCastException: tests.bar cannot be cast to tests.foo
at
org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleException(DefaultConsequenceExceptionHandler.java:39)
at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1283)
at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:1209)
at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1442)
at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:710)
at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:674)
at
org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:230)
at
org.drools.impl.StatelessKnowledgeSessionImpl.execute(StatelessKnowledgeSessionImpl.java:278)
at tests.DroolsTest.testStateless(DroolsTest.java:120)
at tests.DroolsTest.runTest(DroolsTest.java:74)
at tests.DroolsTest.main(DroolsTest.java:59)
Caused by: java.lang.ClassCastException: tests.bar cannot be cast to
tests.foo
at
tests.Rule_find_with_or_411ee1c99de54340945b2b707ad0a576DefaultConsequenceInvoker.evaluate(Unknown
Source)
at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1273)
... 9 more
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