horsdal

  public class UserAggregate : Aggregate
  {
    private readonly UserAggregateProjector projector;
    public string Username { get; internal set; } = String.Empty;
    public string Email { get; internal set; } = String.Empty;

    public UserAggregate()
    {
      this.projector = new UserAggregateProjector(this);
    }

horsdal

  public abstract class Aggregate
  {
    private readonly List<Event> newEvents = new List<Event>();
    public Guid Id { get; internal set; }
    public IEnumerable<Event> NewEvents => this.newEvents.AsReadOnly();

    public void Replay(List<Event> events)
    {
      foreach (var @event in events)
        Play(@event);

horsdal

  public class UserAggregateProjector
  {
    private readonly UserAggregate projection;

    public UserAggregateProjector(UserAggregate projection)
    {
      this.projection = projection;
    }

    protected void When(UserCreatedEvent e)

horsdal

  public class UserAggregate : Aggregate
  {
    public string Username { get; private set; } = String.Empty;
    public string Email { get; private set; } = String.Empty;

    protected void When(UserCreatedEvent e)
    {
      this.Username = e.Username;
      this.Email = e.EmailAddress;
      this.Id = e.Id;

horsdal

    public Task Handle(ChangeUsernameCommand command) =>
      this.helper.Handle(command.Id, aggregate =>
      {
        if (Guid.Empty.Equals(aggregate.Id) || string.IsNullOrWhiteSpace(command.Username))
          return;
        var usernameChanged = new UsernameChangedEvent(command.Username, aggregate.Id, aggregate.Username);
        aggregate.Emit(usernameChanged);
      });

horsdal

  public class ChangeUsernameCommandHandler : IAsyncRequestHandler<ChangeUsernameCommand>
  {
    private readonly CommandHandlersHelper<UserAggregate> helper;

    public ChangeUsernameCommandHandler(CommandHandlersHelper<UserAggregate> helper)
    {
      this.helper = helper;
    }
    
    public Task Handle(ChangeUsernameCommand command) =>

horsdal

  using System;
  using System.Threading.Tasks;

  public class CommandHandlersHelper<T>  where T : Aggregate
  {
    private readonly AggregateRepository repo;
    private readonly EventDispatcher eventDispatcher;

    public CommandHandlersHelper(AggregateRepository repo, EventDispatcher eventDispatcher)
    {

horsdal

  public class UserAggregate : Aggregate
  {
    private string username = String.Empty; 
    private string email = String.Empty;

    public void Create(CreateUserCommand command) { ... } // from the first post
    protected void When(UserCreatedEvent e) { ...  } // from the first post

    public void ChangeUsername(ChangeUsernameCommand command)
    {

horsdal

  using System;
  using System.Threading.Tasks;
  using EventReplay;
  using EventReplay.Infrastructure;
  using MediatR;

  public class ChangeUsernameCommandHandler : IAsyncRequestHandler<ChangeUsernameCommand>
  {
    private readonly AggregateRepository repo;
    private readonly EventDispatcher eventDispatcher;

horsdal

  public class ChangeUsernameCommand : IRequest
  {
    public Guid Id { get; }
    public string Username { get; }

    public ChangeUsernameCommand(Guid id, string username)
    {
      this.Id = id;
      this.Username = username;
    }