[rules-users] Maps in Drools

[Edson Tirelli]

   Yes, that was a bug that was fixed in newer versions of MVEL. Just update
your MVEL jar to 2.0.12.

   []s
   Edson

2009/8/18 André Thieme <address.good.until.2009.dec.14 at justmail.de>

> KDR schrieb:
> > Hi, I'm relatively new to both Java and Drools. I'm trying to figure out
> how
> > to use maps in Drools. I've looked at the thread
> > http://www.mail-archive.com/rules-users@lists.jboss.org/msg09802.html
> >
> >>From what I've read generally it seems best to insert objects directly
> > rather than use nested accessors. So I've been experimenting with trying
> to
> > insert a map and then checking stuff in it.
> >
> > I set up a simple test map of String to Integer, with just "a" as key and
> 1
> > as value, and "b" with 2.
> > Map<String, Integer> map = new HashMap<String, Integer>();
> > map.put("a", 1);
> > map.put("b", 2);
> > String a = "a";
> >
> > I then inserted the map and also inserted the String a of value "a".
> >
> > Here's the test rule, with various things I tried commented out:
> >
> > rule "testing maps"
> >       dialect "mvel"
> >       when
> >               $str: String()
> >               // $m: Map( this[$str] == 1 ) # error
> >               // $m: Map( this.$str == 1 )   # error
> >               // $m: Map( this["$str"] == 1 ) # compiles but rule won't
> fire
> >               $m: Map( this["a"] == 1 ) # this works however!
> >       then
> >               System.out.println($m[$str]); #also works with String and
> Map objects & no
> > conditions
> > end
> >
> > It obviously doesn't like it when I try to use the String object as the
> key
> > for the map. But it works when I use a String literal as the key. What am
> I
> > doing wrong?
> >
> > Does anyone have any suggestions please, or shall I give up and either
> use
> > eval as mentioned in
> > http://www.mail-archive.com/rules-users@lists.jboss.org/msg09716.html or
> use
> > the map as a field of another object which I insert instead of the map
> (in
> > fact that was my original plan!)?
>
> In exactly this thread Marc answered to that problem.
> http://www.mail-archive.com/rules-users@lists.jboss.org/msg09837.html
>
> His first idea is that this is a bug in the mvel dialect.
> I tried exactly that. I had a global var and put the string "a" into it.
> Then I wanted to check if Map( this[myVar] == 1 ) but this didn't work.
>
>
> > I'd also need to test for null i.e. whether a key/value pair exists for a
> > given String as the key.
>
> This seems to be only true when you go the route that I go, namely using
> the default rule syntax, i.e., eval.
>
>
> Sunny greetings,
> André
> --
> Lisp is not dead. It’s just the URL that has changed:
> http://clojure.org/
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>



-- 
 Edson Tirelli
 JBoss Drools Core Development
 JBoss by Red Hat @ www.jboss.com
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