[rules-users] Clarification of using collections as facts

[Bagwell, Allen F]

A-HA!

Thank you!

I figured I was making things overly complicated.

:-)
-Allen

________________________________
From: rules-users-bounces at lists.jboss.org [mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Edson Tirelli
Sent: Friday, July 18, 2008 8:55 AM
To: Rules Users List
Subject: Re: [rules-users] Clarification of using collections as facts


   Hi all, sorry for the long absence. I'm back, but I know no one noticed, anyway... ;)

   Allen, not really. Collections usually are not asserted as standalone facts because they lack semantic meaning. They are abstractions, if you know what I mean.

   So, in your case, you can write patterns like this:

Foo( names contains "abc" )
Foo( names not contains "abc" )

    Now, a regexp will act over Strings, not collections. So if you want to write a rule that acts on each name that matches a regexp, you must "iterate" over your collections elements using the "from" CE:

Foo( $names : names )
String( this matches "error.*" ) from $names

    Now, if you want the rule to re-create a new list containing only the names matching a pattern, THEN you may use the collect CE to create a collection:

$foo : Foo( $names : names )
$foundThese : ArrayList( ) from collect( String( this matches "error.*" ) from $names )

   You may also filter your resulting collection to only fire the rule when there are actual elements. Just for the sake of examples, since you are already binding $foo, you don't need to bind $names too:

$foo : Foo( )
$foundThese : ArrayList( size > 0 ) from collect( String( this matches "error.*" ) from $foo.names )

    Happy drooling,
          Edson


2008/7/15 Bagwell, Allen F <afbagwe at sandia.gov<mailto:afbagwe at sandia.gov>>:

I'm going through the Drools documentation regarding the use of lists and other collections. I want to make sure my understanding is correct.

So if I have a class:

public class Foo {

   private int x;
   private int y;
   private List<String> names = ArrayList<String>();

   public List<String> getNames() {return names;}

   // appropriate getters/setters for the int fields ...
}

With this I can insert a Foo object into working memory. I can even make the int fields dynamic facts with the appropriate addition of "bean-ifying" code.

For the List, however, I need to insert it separately into working memory in order to make use of Drools' rule language ('contains' ,etc.)? I'm assuming that doesn't come free because I have to insert my own custom class objects if they are included via composition in a larger fact!

Also, I'm guessing the Collection type classes cannot be dynamic facts? Meaning if I modify my List with add, remove,  clear, etc., I must explicitly call update in my code on the List fact in order to alert Drools to a change in the List, correct?

So then the question also comes up as to how I would write a rule that looks for all instances of Strings in the List that match against a given regex expression. I've not been successful at figuring this out...

Rule "when a Foo List is modified, get all Strings in it that start with 'error'"
when
   $foo : Foo($names : names)
   $foundThese : ArrayList() from collect(??? matches "error.*" from $names)
then
   // act on $foo and $foundThese

I know that rule is NOT correct, but I'm not sure how I'm supposed to access an immutable object inside a collection. The examples in the documentation show how to get at mutable class objects.


Thanks!
-Allen





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--
Edson Tirelli
JBoss Drools Core Development
JBoss, a division of Red Hat @ www.jboss.com<http://www.jboss.com>
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