Re: [rules-users] Can only reason over sub-objects if you use the FromConditional Element
Hello, Mike,
The behavior is identical whether I update the sub-object or not --
the "good" rule always works as long as I update the root person
object AND the "bad" rule will not work even if I explicitly update
the sub-object as you've suggested.
This leads me to interpret the engine behavior as:
1) An update() to a root object is enough to communicate to the rules
engine that the entire object graph has (potentially) changed
2) The engine will properly reason over sub-objects only if you use
the From conditional element (but not if you use MVEL sub-property
expressions)
So if (1) is the intended behavior of the engine, then my question is
still this... is (2) a necessary constraint? Shouldn't the engine be
able to reason over MVEL sub-property expressions without requiring
the From conditional element? If so, it makes for a more direct syntax
to allow MVEL sub-property expressions in the LHS, doesn't it?
Thanks in advance for any help on this!
Aaron
On Mon, Mar 17, 2008 at 4:08 AM, Anstis, Michael (M.) <manstis1(a)ford.com> wrote:
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(a)lists.jboss.org
[mailto:rules-users-bounces@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
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