Comparing a field in a List of objects with a List of Strings in Drools

Question

Assume I have a Policy object in Drools, that object contains a List of Cover objects, called covers and a List of String objects, which are called requestedCovers.

The Cover object contains type field, which is a String object.

I want to fire a rule if a requestedCover does not match a type in the Covers list.

rule "Add validation error for policies with requested covers that are not available"
when
    $p: Policy(available == true, $requestedCovers: requestedCovers, $covers: covers)
    $requestedCover: String() from $requestedCovers
    Cover(type not contains $requestedCover) from $covers 
then
    log.error("RHS rule not implemented yet. Found type {}.", $requestedCover);
end

However this seems to trigger every Cover is the covers list.

How to create this rule?

score 1 · Accepted Answer · answered Jul 31 '17 at 10:10

Finally figured it out, thanks to @laune for the help

when
    $p: Policy(available == true, $requestedCovers: requestedCovers, $covers: covers)
    $requestedCover: String() from $requestedCovers
    $coverTypes: List(!this.isEmpty()) from accumulate(Cover($coverType: type) from $covers; collectList($coverType))
    eval(!$coverTypes.contains($requestedCover))

laune · Answer 2 · 2017-07-19T09:17:45.147

0

You have two lists in this unwieldy object, and one of them is a cut of another list. What you need is the set of requestedCovers - covers.type (a set difference).

It's a cinch to write the set difference as a method, either in Policy or (as a static) in a separate utility class.

If you insist on Drools, you'll have to

rule x
when
  Policy( available, $reqs: requestedCovers, $covs: covers )
  accumulate( Cover( $type: type ) from $covs;
              $covered: collectSet( $type ) )
  $s: String( this not memberOf $covered ) from $reqs
then
  ...$s is not covered...
end

Untested!

edited Jul 19 '17 at 09:17

answered Jul 17 '17 at 13:43

laune

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Okay. Looks promissing. It first complained about `mismatched input 'not' in rule`. After changing `not in` to `not memberOf`. Now it is complaining about `Unknown property: type`. Any idea? – Martijn Burger Jul 17 '17 at 14:55
OK, sorry, I fixed the `not in`. - But if `type` isn't known, I cannot see why. Does class Cover contain a `public String getType()`? – laune Jul 19 '17 at 09:20
Yes. Case has a String getType() accessor method. – Martijn Burger Jul 21 '17 at 09:23
`Case` or `Cover`? – laune Jul 21 '17 at 19:14
Sorry I meant `Cover`. – Martijn Burger Jul 23 '17 at 19:31
I guess then we are down to: please provide a full set of code reproducing the problem. – laune Jul 25 '17 at 16:32
Yeah, I understand. Let me look into it first. I agree that it's a stange error, so I'll look if I can pinpoint it a bit further down. – Martijn Burger Jul 26 '17 at 13:00
Thanks for the help! Figured it out, see my answer. – Martijn Burger Jul 31 '17 at 10:11
And now it is not complaining about `type` being unknown? That's very strange. – laune Jul 31 '17 at 11:29

Comparing a field in a List of objects with a List of Strings in Drools

2 Answers2