Apologies, I should have given the error message I get with $m: Map(
this[$str] == 1 ) and also with $m: Map( this.$str == 1 ) -
org.drools.RuntimeDroolsException: Exception executing predicate this[$str]
== 1
and lots more lines followed by -
Caused by: [Error: unable to resolve method: java.util.HashMap.$str()
[arglength=0]]
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.