Why should you care?

ShopNest wants consistent validation/logging on every command without copy-paste.

See it live — copy this example

Paste into a C# console or class library project and run dotnet run.

public interface IPipelineBehavior<TRequest, TResponse>
{
    Task<TResponse> Handle(TRequest request, Func<Task<TResponse>> next);
}
public sealed class LoggingBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
{
    public async Task<TResponse> Handle(TRequest request, Func<Task<TResponse>> next)
    {
        Console.WriteLine($"start {typeof(TRequest).Name}");
        var response = await next();
        Console.WriteLine($"end {typeof(TRequest).Name}");
        return response;
    }
}

// mediator pipeline: logging -> validation -> handler
Console.WriteLine("pipeline: log → validate → PlaceOrderHandler");

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• Behaviors form a chain around the handler.
• This is the MediatR-specific deep dive beyond basic Send/Handle.

Practice next

1. Add LoggingBehavior in a real MediatR app.
2. Add ValidationBehavior throwing on invalid commands.
3. Order behaviors deliberately.
4. Add timing behavior with Stopwatch.
5. Short-circuit validation failures.

Remember

Middleware for handlers. Cross-cutting in one place. Handlers stay pure.

ShopNest MediatR behaviors

All commands get validation + logging.

Outcome: Consistent ops without handler clutter.