I am trying to find the total of an attribute of`SubjectTeacherPeriod`. The `numAttributeMap`property (a map with `String` keys and `int` values) stores the value. But trying to access it is problematic as Drools thinks that `$num_value[$attribute]` is a list operation, not a map operation. I listed my rule and runtime errors: rule "insertAttributeDayTotal" //salience 1 // Do these rules first (optional, for performance) when $sum_regression_constraint : SumRegressionConstraint( $class : class_, $attribute : attribute//, //$weight : weight; ) $day_of_week : DayOfWeek() $attribute_day_total : Number() from accumulate( SubjectTeacherPeriod( //period != null, period.class_ == $class, period.dayOfWeek == $day_of_week, $num_value : numAttributeMap //$total : num_attribute_map.get($attribute) ), sum($num_value[$attribute]) //PROBLEM LINE?? ) then //System.out.println("BUCKET TOTAL "+$id+" "+$bucket_total.intValue()); insertLogical(new AttributeDaySum($class, $attribute, $day_of_week, $attribute_day_total.intValue())); end *Errors:* jesvin@Jesvin-Technovia:~/dev/drools/timetabler$ java -server in.co.technovia.timetabler.TimeTableApp Exception in thread "main" java.lang.IllegalStateException: There are errors in the scoreDrl's: Rule Compilation error : [Rule name='insertAttributeDayTotal'] in/co/technovia/timetabler/domain/Rule_insertAttributeDayTotal_fd3f7d4f98084049887c1596f5a56805.java (9:1093) : The type of the expression must be an array type but it resolved to Map in/co/technovia/timetabler/domain/Rule_insertAttributeDayTotal_fd3f7d4f98084049887c1596f5a56805.java (9:1104) : Type mismatch: cannot convert from String to int at org.drools.planner.config.solver.SolverConfig.buildRuleBase(SolverConfig.java:238) at org.drools.planner.config.solver.SolverConfig.buildSolver(SolverConfig.java:170) at org.drools.planner.config.XmlSolverConfigurer.buildSolver(XmlSolverConfigurer.java:103) at in.co.technovia.timetabler.TimeTableApp.createSolver(TimeTableApp.java:55) at in.co.technovia.timetabler.TimeTableApp.main(TimeTableApp.java:39) -- View this message in context: http://drools.46999.n3.nabble.com/Drools-Planner-getting-confused-between... Sent from the Drools: User forum mailing list archive at Nabble.com.