Identify the first or last of a fact

[douglasg14b]

Lets say you have a stream of events, and in that stream you will have multiple facts that will trigger the same rule.

I have a stream of events and some events will trigger the same rules multiple times, adding similar facts multiple times. For instance, messages in a conversation.

I thought I could do this with queries by specifying an order and then using LINQ First() or Last() but those do not appear to be available?

How can I select the first or last of a set of facts?

I thought maybe I could do this via:

public class LatestExpertAssignmentRule : Rule
{
    public override void Define()
    {
        AssignedToExpertFact assignment = null!;
        L1TwilioTaskRouterEvent? reservationAccepted = null;

        When()
            .Match(() => reservationAccepted!, x => x.EventType == "reservation.accepted")
            .Query(() => assignment, x => x
                .Match<AssignedToExpertFact>()
                .Collect()
                .OrderBy(a => a.Timestamp)
                .Where(a => a.Any())
                .Select(a => a.Last())
            );

        Then()
            .Yield(_ => new LatestAssignmentFact(assignment));
    }
}

But Fire() throws:

NRules.RuleRhsExpressionEvaluationException: Failed to evaluate rule action
(_, assignment) => {var Param_0; ... }
RemoteExpertData.Features.RulesEngine.Rules.LatestExpertAssignmentRule
---> System.ArgumentException: An item with the same key has already been added. Key: LatestAssignmentFact

I'm not really sure what to do here 🤔 Been running into a lot of gotchas along the way, maybe this is another one?

[douglasg14b]

Closing as removing the .Match(() => reservationAccepted!, x => x.EventType == "reservation.accepted") which I seemed to just blindly glance over fixed the issue. As that was causing it to match many times when it didn't need to.