LuckyPennySoftware/MediatR · info · ArgumentException

Name cannot be '2'

Error message

Name cannot be '2'

What it means

Intentional demo throw inside a sample notification handler. The sample deliberately raises ArgumentException when the handler was constructed with the name "2", to showcase how each PublishStrategy (sync/async/parallel) propagates handler exceptions. It is not a library invariant; it is a scripted fault injected for the PublishStrategies sample.

Source

Thrown at samples/MediatR.Examples.PublishStrategies/AsyncPingedHandler.cs:20

using System.Threading;
using System.Threading.Tasks;

namespace MediatR.Examples.PublishStrategies;

public class AsyncPingedHandler : INotificationHandler<Pinged>
{
    public AsyncPingedHandler(string name)
    {
        Name = name;
    }

    public string Name { get; set; }

    public async Task Handle(Pinged notification, CancellationToken cancellationToken)
    {
        if (Name == "2")
        {
            throw new ArgumentException("Name cannot be '2'");
        }

        Console.WriteLine($"[AsyncPingedHandler {Name}] {DateTime.Now:HH:mm:ss.fff} : Pinged");
        await Task.Delay(100).ConfigureAwait(false);
        Console.WriteLine($"[AsyncPingedHandler {Name}] {DateTime.Now:HH:mm:ss.fff} : After pinged");
    }
}

View on GitHub (pinned to 916ef1b3d6)

Solutions

1. If you only want successful runs, construct AsyncPingedHandler with a name other than "2" (or remove that registration from the sample's DI setup).
2. If you are studying error propagation, leave it as-is and await the Publish call so the strategy surfaces the exception (AggregateException for WhenAll, first exception for StopOnException).
3. If you adapted this sample into production code, delete the `if (Name == "2")` block entirely; it exists purely for the demo.

Example fix

// before
new AsyncPingedHandler("2") // throws on Handle
// after
new AsyncPingedHandler("0") // runs normally

// Validate the handler name before relying on the sample's fault-injection contract
if (handler is AsyncPingedHandler a && a.Name == "2")
    throw new InvalidOperationException("AsyncPingedHandler(\"2\") is a demo fault; use another name.");

When it happens

Trigger: An instance of AsyncPingedHandler created with the constructor argument "2" is resolved and invoked by MediatR when a Pinged notification is published. The check `if (Name == "2")` fires on entry to Handle before any logging or delay.

Common situations: Running or copying the MediatR.Examples.PublishStrategies sample where handlers are wired with names "0","1","2",...; this handler is expected to throw so you can observe how ParallelWhenAll / SyncStopOnException etc. aggregate the failure.

Related errors

• Name cannot be '2'
• Unknown strategy: {strategy}

AI-assisted analysis of LuckyPennySoftware/MediatR@916ef1b3d6 (2026-08-13). Data as JSON: /api/errors/94ecd8e7968817d8. Report an issue: GitHub.