[rules-users] Can only reason over sub-objects if you use the FromConditional Element

[Anstis, Michael (M.)]

IMO, you have not informed the engine\RETE network that details have changed
in your first example.

This would probably be a better example:-

rule "30 is the new 20"
when
	person : Person( $d : details.age == 30 )
then
	person.getDetails().setAge(20);
	System.out.println( "Now 20 : " + person );
	update( person );
	update( $d );
end
 
The From works because it gets external data rather than using that already
in the engine\RETE network.

IMO, I think the rules are working correctly; it's just a misunderstanding
of how the engine\RETE network function.

I hope this helps.

Thanks,

Mike

-----Original Message-----
From: rules-users-bounces at lists.jboss.org
[mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Aaron Dixon
Sent: 14 March 2008 20:51
To: Rules Users List
Subject: [rules-users] Can only reason over sub-objects if you use the
FromConditional Element

It appears that you MUST use the From Condition Element to reason over
sub-objects.

I have a Person class. Person::getDetails() returns a Details
instance, which has the name and age of the person. (This is a
contrived example to demonstrate the issue.)

My rules are:

rule "30 is the new 20"
when
	person : Person( details.age == 30 )
then
	person.getDetails().setAge(20);
	System.out.println( "Now 20 : " + person );
	update( person );
end

rule "Older than 20 - Good"
salience -100
when
	person : Person( )
	Details( age > 20 ) from person.details
then
	System.out.println( "Older than 20 (good) : " + person );
end

rule "Older than 20 - Bad"
salience -100
when
	person : Person( details.age > 20 )
then
	System.out.println( "Older than 20 (bad) : " + person );
end

I assert Abe, Bob, Cat, Don, and Eve with ages of 10, 20, 30, 40, and
50, respectively. The output is as follows.

Now 20 : Person(Details(Cat,20))
Older than 20 (good) : Person(Details(Eve,50))
Older than 20 (bad) : Person(Details(Eve,50))
Older than 20 (good) : Person(Details(Don,40))
Older than 20 (bad) : Person(Details(Don,40))
Older than 20 (bad) : Person(Details(Cat,20))


You can see that the "Bad" rule is more concise but it does not use
the From Conditional Element and therefore it doesn't work properly
(Cat is determined to be older than 20 when she is not.)

Why does Drools allow the "Bad" rule to be written and compiled when
it does not behave properly?

Thanks,
Aaron
_______________________________________________
rules-users mailing list
rules-users at lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/x-pkcs7-signature
Size: 7206 bytes
Desc: not available
Url : http://lists.jboss.org/pipermail/rules-users/attachments/20080317/9d5284c4/attachment.bin