在Drools对象的所有日期中查找最近的日期

Question

How can I find the most recent date among all joining dates in a Drools object?

My rule is something like this:

declare RecentDate
      dates : java.util.Date
end

rule "insert_dates"
      when
       //reading dates from back end
       Employee($date : dateOfJoining, $name : name, salary > 10000)
       then
       insert(new RecentDate($date))
end

Now I would like to find the most recent employee based on dateOfJoining. Any help is appreciated. Thank you.

Answer 1

One way to do it is to, given an employee, make sure that there is no other with a higher date:

declare RecentDate
      dates : java.util.Date
end

rule "insert_dates"
when
  //reading dates from back end
  Employee( $date : dateOfJoining, $name : name, salary > 10000)
  not Employee (dateOfJoining > $date)
then
  insert(new RecentDate($date))
end

The rule above only works on the case you have all your Employee facts in your session before you execute fireAllRules() . If this is not the case, you can try to initially insert a RecentDate with a null date and then compare each Employee against it and update it accordingly:

rule "Init RecentDate"
when
  not RecentDate()
then
  insert new RecentDate(null);
end

rule "update_dates"
when
  Employee( $date : dateOfJoining, $name : name, salary > 10000)
  $d: RecentDate ( date == null || date < $date)
then
  modify ($d){
    setDate($date)
  }
end

Hope it helps,