Checking if an object of a list has some value with drools

问题

I have some problems checking if an object of a list has a value with drools.

My model is this

class Products{
    private List<Approver> approvalPath;
}
class Approver{
    private String employeeName;
}

So, I need to make a rule like this

rule "member"
    when
        //approvalPath has an approver with name "Charles" (for example)
    then
        //do something
end

How can I do it?

回答1:

Here are two versions.

when
  $app: Approver( employeeName == "Charles" )
  Products( approvalPath contains $pp )

And:

when
  Products( $ap: approvalPath )
  Approver( employeeName == "Charles" ) from $ap

Number 1 requires the insertion of Approver objects as facts.

回答2:

rule member
when
    $p : Products()
    $a : Approver( name == "Charles" ) from $p.approvalPath
then
...
end

The above rule will fire once for each Approver named Charles in the list. If you want to fire the rule just once, no matter how many approvers named Charles are in the list, just wrap the second line in exists( ... ).

来源：https://stackoverflow.com/questions/22257132/checking-if-an-object-of-a-list-has-some-value-with-drools