ChangeCustomerPricingLevel.cs

using System;
using System.Threading.Tasks;
using MediatR;
using Nancy;
using Nancy.ModelBinding;

namespace ThinControllers.Demo.ChangeCustomerPricingLevel
{
    public class Module : NancyModule
    {
        public Module(IMediator mediator)
        {
            Put["/demo/changepricinglevel/{MessageId:Guid}", true] = async (parameters, token) =>
            {
                var cmd = this.Bind<Command>();
                var envelop = new Envelope<Command>((Guid)parameters.MessageId, cmd);
                await mediator.SendAsync(envelop);

                return HttpStatusCode.NoContent;
            };
        }
    }

    public class Command : IAsyncRequest
    {
        public Guid CustomerId { get; }
        public PricingLevel PricingLevel { get; }

        public Command(Guid customerId, PricingLevel pricingLevel)
        {
            CustomerId = customerId;
            PricingLevel = pricingLevel;
        }
    }

    public class Handler : IAsyncRequestHandler<Envelope<Command>, Unit>
    {
        private readonly CustomeRepository _repository;

        public Handler(CustomeRepository repository)
        {
            _repository = repository;
        }

        public async Task<Unit> Handle(Envelope<Command> message)
        {
            var customer = _repository.Get(message.Body.CustomerId);
            try
            {
                customer.SetOperation(message.MessageId);
            }
            catch (InvalidOperationException)
            {
                return Unit.Value;
            }

            customer.ChangePricingLevel(message.Body.PricingLevel);
            await _repository.SaveAsync(customer);

            return Unit.Value;
        }
    }
}