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

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.