[rules-users] Searching for an object in a list inside a map

[Steinmetz, Jean-Philippe]

Hello,

I have a scenario where I have a rule that is searching for a particular
object inside a list and the list is an entry in a hashmap.

An example of the class structure looks something like this.

class Player {
  String name;
}

class TeamRoster {
  // Maps team name to players
  Map<String, List<Player>> teams;
}

The goal of the rule is to activate when there is a player named John on
the Dodgers team. I have tried writing rules a couple of ways but end up
with errors using either approach. My first approach was the following:

dialect "mvel"
rule
when
  $roster : TeamRoster()
  $player : Player(name == "John") from $roster.teams["Dodgers"]
then
  ...
end

However this resulted in the following error:
Unable to Analyse Expression $roster.teams["Dodgers"]:
sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl cannot be cast
to java.lang.Class]

So I tried changing it up with the following...

dialect "mvel"
rule
when
  $roster : TeamRoster()
  $player : Player(name == "John")
  eval($roster.teams["Dodgers"] contains $player
then
  ...
end

This effectively yields the same error:
Expression $roster.teams["Dodgers"] contains $player:
sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl cannot be cast
to java.lang.Class]

Note I am using Drools 6.0.1.Final. Is this some sort bug or limitation
with the rules parser? Assuming I cannot change the class structure how can
I achieve what I need?

Thanks in advance,

Jean-Philippe Steinmetz
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