My colleague has confirmed that this behavior has been around since Drools 4, and it continues to be a problem for Drools 5.0.1 and 5.1.0.M1, assuming it's a problem and not working as intended.
 
$fact.setPath("...") implements the correct PropertyChangeSupport mechanism for Drools.  At least Drools is using it and responding mostly as expected.
 
This runs once:

rule "Constrain to owner or published to public"

when

$fact : ListFact(

$path : path not matches ".*owner.*",

noopResponse == true

)

$model : Model()

then

modify($fact)

{

setPath($fact.getPath() + "[owner]")

}

update($fact);

end

 
This runs twice:

rule "Constrain to owner or published to public"

when

$fact : ListFact(

$path : path not matches ".*owner.*",

noopResponse == true

)

$model : Model()

then

modify($fact)

{

setPath($fact.getPath() + "[owner]")

}

end

 
If I don't use modify(...) and simply change the $fact bean path property, the same thing occurs.  If I explicitly call update($fact), the rule runs once.  If I don't it runs twice.
 
I get "/path[owner][owner]" when I actually wanted "/path[owner]", because it ran twice, not once.
 
Why doe update(...) work differently from the PropertyChangeSupport mechanism???  Shouldn't I be able to depend on Drools to run this rule only one time?
 
I am, admittedly, a bit of a noob at this, but I ran this by my local Drools resident expert, and he doesn't know the answer either.
 
Thanks so much!
 

Jason Smith
Software Engineer
InfoTrust Group, Inc.

500 Discovery Parkway, Suite 200
Superior, CO 80027
Office 303-627-6571
Fax 303-666-6711
Email jsmith@infotrustgroup.com

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