How to get the name of an event?

[crashkonijn]

Hi,

First of all, thanks for making this open source software!

I've been playing around with Elsa and trying to learn how to do certain things.

I'm trying to make a "multi trigger", where you can setup multiple events and based on which one is triggered you continue among different paths.

Based on the FlowSendHttpRequest I've managed to make the following activity:

public class MultiEventActivity : Activity, IActivityPropertyDefaultValueProvider
{
    [Input(
        Description = "A list of expected status codes to handle.",
        UIHint = InputUIHints.DynamicOutcomes,
        DefaultValueProvider = typeof(MultiEventActivity),
        Order = 5.1f
    )]
    public Input<ICollection<string>> Events { get; set; } = default!;

    protected override ValueTask ExecuteAsync(ActivityExecutionContext context)
    {
        foreach (var evt in this.Events.Get(context))
        {
            context.WaitForEvent(evt, EventReceivedCallback);
        }

        return default;
    }

    private ValueTask EventReceivedCallback(ActivityExecutionContext context)
    {
        Console.WriteLine("signal received");

        var eventInput = context.GetEventInput();
        
        // context.WorkflowExecutionContext.
        
        return default;
    }

    public object GetDefaultValue(PropertyInfo property)
    {
        if (property.Name == nameof(Events))
        {
            return new List<string>
            {
                "done"
            };
        }

        return null!;
    }
}

I just can't figure out how to get the name of the event that was triggered in the EventReceivedCallback method. Is this possible?

I could add an extra input to the event trigger, but that seems like an unnecessary workaround:

// POST /elsa/api/events/{eventName}/trigger
{
"Input": { "event": "{eventName}" }
}

Thanks in advance!

[sfmskywalker]

Short answer: not directly from ActivityExecutionContext in that callback.

In the current event API:

• WaitForEvent(eventName, callback) stores the event name in the bookmark stimulus as new EventStimulus(eventName).
• GetEventInput() only reads the payload from Event.EventInputWorkflowInputKey in workflow input.
• EventBase<TResult>.EventReceivedAsync also only forwards the payload/result, not the matched event name.

Relevant source:

• elsa-core/src/modules/Elsa.Workflows.Runtime/Extensions/ActivityExecutionContextEventExtensions.cs
• elsa-core/src/modules/Elsa.Workflows.Runtime/Activities/EventBase.cs
• elsa-core/src/modules/Elsa.Workflows.Runtime/Activities/Event.cs
• elsa-core/src/modules/Elsa.Workflows.Runtime/Services/EventPublisher.cs

So I don’t see a built-in GetTriggeredEventName()-style API on the callback context.

If you need to know which event fired, the repo-backed options I can see are:

• include the event name in the payload when publishing the event, or
• model each event as a separate activity/branch so the execution path itself identifies the event.

So your workaround idea is not unnecessary in the current implementation; it is the straightforward way to propagate the event identity to the callback.