规则编译错误：只能迭代java.lang.Iterable的数组或实例

Question

I am new to mongoDb and drools. I am writing a rule in drools, which is iterating a java list. But when running tomcat it is giving Rule Compilation error.

Getting List from dao :-

List<XYZ> list = new ArrayList<XYZ>();
Query q = query(where("id").is(userId));
list = getMongoOperation().find(q, XYZ.class, "XYZ"); 

Using list in drools engine Rule :-

for(XYZ xyzObj : list) 
{           
}

Model Class :-

@Document(collection="XYZ")
public class XYZ 
{
}

I am getting exception when running tomcat. "Rule Compilation error : Can only iterate over an array or an instance of java.lang.Iterable"

Rule File :-

import java.util.List; import java.util.Iterator; global com.demo.XYZ list

rule '1_Demo_Rule'

when prop : RULEDEMO( attribute == "demo") then

  for(XYZ xyzObj : list) { } 

end

Answer 1

You will not be able to use the short syntax of the for-statement at all, due to restrictions in the DRL parser.

Given that

global List<com.demo.XYZ> list;

use the not-so-nice

for( int i = 0; i < list.size(); i++ ){
    XYZ xyzObj = list.get(i);
    // ...
}