[rules-users] MVEL syntax String as key for maps Re: Maps in Drools

[KDR]

Just to report back. Downloading the mvel2-2.0.14-SNAPSHOT.jar and renaming
it to mvel2-2.0.10.jar in my Drools runtime folder (top level and lib) while
renaming the old mvel2-2.0.10.jars to something else. got this to work:
$m: Map( this[$str] == 1 )

However, although the MVEL page at
http://mvel.codehaus.org/MVEL+2.0+Property+Navigation says
   "For Maps that use a String as a key, you may use another special syntax:
   user.foobar"
I found that 
$m: Map( this.$str == 1 )
still produces the same error as before.

I don't know if this is only because that particular special MVEL syntax is
not supported in Drools (obviously it's not a major thing as [$str] works),
or because there's still a bug there. Just thought I ought to mention it in
case it's a bug.

Cheers.


KDR wrote:
> 
> 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!)?
> 
> I'd also need to test for null i.e. whether a key/value pair exists for a
> given String as the key.
> 
> Any thoughts would be very much appreciated.
> 
> Many thanks in advance.
> 

-- 
View this message in context: http://www.nabble.com/Maps-in-Drools-tp25031348p25066578.html
Sent from the drools - user mailing list archive at Nabble.com.