DDD, CQRS, Event-Driven, Actor Model and Microservices

I want to share my experience in implementing microservice architecture on top of actor-model frameworks such as AKKA and Microsoft Orleans.

My hypothesis: if you use one stack to implement microservices, then you can:

• Dramatically reduce development complexity and code size
• Simplify debugging and troubleshooting
• Simplify deployment
• Simplify the task of defining service boundaries
• Get rid of the limitation of the use of stateful services
• Simplifies the work with distributed transactions.

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public class UserId : Identity<UserId>
{
    public UserId(System.String value) : base(value) { }
}
[Validator(typeof(BirthValidator))]
public class Birth : SingleValueObject<DateTime>
{
    public Birth(DateTime value) : base(value) { }
}
public class BirthValidator : AbstractValidator<Birth>
{
    public BirthValidator()
    {
        RuleFor(p => p.Value).NotNull();
        RuleFor(p => p.Value).LessThan(DateTime.Now);
    }
}

[Description("  ")]
[HasPermissions(DemoContext.CreateUser, DemoContext.ChangeUser)]
[Validator(typeof(CreateUserCommandValidator))]
public class CreateUserCommand : Command<UserId>
{
    public LocalizedString UserName { get; }
    public Birth Birth { get; }

    public CreateUserCommand(UserId aggregateId, LocalizedString userName, Birth birth) : base(aggregateId)
    {
        UserName = userName;
        Birth = birth;
    }
}

public class CreateUserCommandValidator : AbstractValidator<CreateUserCommand>
{
    public CreateUserCommandValidator(IServiceProvider sp)
    {
        RuleFor(p => p.AggregateId).NotNull();
        RuleFor(p => p.UserName).SetValidator(new UserNameValidator());
        RuleFor(p => p.Birth).ApplyRegisteredValidators(sp);

    }
}
[Validator(typeof(BirthValidator))]
public class Birth : SingleValueObject<DateTime>
{
    public Birth(DateTime value) : base(value) { }
}
public class BirthValidator : AbstractValidator<Birth>
{
    public BirthValidator()
    {
        RuleFor(p => p.Value).NotNull();
        RuleFor(p => p.Value).LessThan(DateTime.Now);
    }
}
public class UserState : AggregateState<UserState, UserId>,
    IApply<UserCreatedEvent>,
    IApply<UserRenamedEvent>,
    IApply<UserNotesChangedEvent>,
    IApply<UserTouchedEvent>,
    IApply<ProjectCreatedEvent>,
    IApply<ProjectDeletedEvent>
{
    public LocalizedString Name { get; private set; }
    public Birth Birth { get; private set; }
    public System.String Notes { get; private set; } = System.String.Empty;
    public IEnumerable<Entities.Project> Projects => _projects;

    public void Apply(UserCreatedEvent e) { (Name, Birth) = (e.Name, e.Birth); }
    public void Apply(UserRenamedEvent e) { Name = e.NewName; }
    public void Apply(UserNotesChangedEvent e) { Notes = e.NewValue; }
    public void Apply(UserTouchedEvent _) { }

    public void Apply(ProjectCreatedEvent e)
    {
        _projects.Add(new Entities.Project(e.ProjectId, e.Name));
    }

    public void Apply(ProjectDeletedEvent aggregateEvent)
    {
        var projectToRemove = _projects.FirstOrDefault(i => i.Id == aggregateEvent.ProjectId);
        if (projectToRemove != null) _projects.Remove(projectToRemove);
    }

    private readonly ICollection<Entities.Project> _projects = new List<Entities.Project>();
}
public class UserAggregate : EventDrivenAggregateRoot<UserAggregate, UserId, UserState>,
    IExecute<CreateUserCommand, UserId>,
    IExecute<ChangeUserNotesCommand, UserId>,
    IExecute<TrackUserTouchingCommand, UserId>
{
    public UserAggregate(UserId id) : base(id)
    {
        Command<RenameUserCommand>();
        Command<CreateProjectCommand>();
        Command<DeleteProjectCommand>();
    }

    internal async Task CreateProject(ProjectId projectId, ProjectName projectName)
    {
        await Emit(new ProjectCreatedEvent(Id, projectId, projectName));
    }

    internal async Task DeleteProject(ProjectId projectId)
    {
        await Emit(new ProjectDeletedEvent(Id, projectId));
    }

    public async Task<IExecutionResult> Execute(CreateUserCommand cmd)
    {
        //SecurityContext.Authorized();
        //SecurityContext.HasPermissions(cmd.AggregateId, DemoContext.TestUserPermission);

        await Emit(new UserCreatedEvent(cmd.UserName, cmd.Birth));
        return ExecutionResult.Success();
    }

    public async Task<IExecutionResult> Execute(ChangeUserNotesCommand cmd)
    {
        await Emit(new UserNotesChangedEvent(Id, State.Notes, cmd.NewValue));
        return ExecutionResult.Success();
    }

    public async Task<IExecutionResult> Execute(TrackUserTouchingCommand cmd)
    {
        await Emit(new UserTouchedEvent());
        return ExecutionResult.Success();
    }

    public async Task Rename(UserName newName)
    {
        await Emit(new UserRenamedEvent(newName));
    }
}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

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Simplify the work with distributed transactions

Stateful out-of-the-box sagas allow you to create distributed transactions.

Some example implementation can be viewed here .