Email notifications. In a domain object or service?

Question

I am looking for recommendations on how to approach the next design problem (using a dummy example based on stackoverflow). I would try to avoid the anemic domain model and look for general “best practical” advice for this type of case.

Scenario:

Suppose a new feature is being developed for stackoverflow, which sends an email notification to the question owner whenever 10 upvotes receive his / her question.

The domain object model looks something like this:

public class Question
{
    string Question { get; set; }
    IList<Votes> Upvotes { get; set; }
    User Owner { get; set; }

    public void AddUpvote(Vote upvote)
    {
        Upvotes.Add(upvote);
    }
}

Potential implementations:

• Change AddUpvote()to take the parameter IEmailerServiceand execute the logic in the method AddUpvote().

  public void AddUpvote(Vote upvote, IEmailerService emailer)
  {
      Upvotes.Add(upvote);
      if ( Upvotes.Count == 10 )
      {
          emailer.Send(Owner.EmailAddr);
      }
  }
  

• AddUpvote() AddUpvote() IEmailService IoC ( IEmailerService ).

• , question.AddUpvote().

  public void UpvoteClickHandler(Question question)
  {
      question.AddUpvote(new Upvote());
      if ( question.Upvotes.Count == 10 )
      {
          _emailer.Send(question.Owner.EmailAddr);
      }
  }
  

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Answer 1

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public class Question
{
    public string Description { get; set; }
    public Int32 Votes { get; set; }
    public User Owner { get; set; }

    public event EventHandler<QuestionEventArgs> OnUpvote;

    private void RaiseUpvoteEvent(QuestionEventArgs e)
    {
        var handler = OnUpvote;
        if (handler != null) handler(this, e);
    }

    public void Upvote()
    {
        Votes += 1;

        RaiseUpvoteEvent(new QuestionEventArgs(this));
    }
}

public class MessageService
{
    private Question _question;

    public MessageService(Question q)
    {
        _question = q;

        q.OnUpvote += (OnUpvote);
    }

    private void OnUpvote(object sender, QuestionEventArgs e)
    {
        if(e.Question.Votes > 10)
            SendMessage(e.Question.Owner);
    }
}

public class QuestionEventArgs: EventArgs
{
    public Question Question { get; set; }

    public QuestionEventArgs(Question q)
    {
        Question = q;
    }
}

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Answer 2

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NotificationManager ( , ).

public Class NotificationManager
{
    public void NotificationManager(NotificationPolicy policy, IEmailService emailer)
    {
    }
}

- (UpvoteClickHandler NotificationManager):

public void UpvoteClickHandler(Question question)
{
    question.AddUpvote(new Upvote());
    _notificationManager.Notify(Trigger.UpvoteAdded, question);
}

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Answer 3

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Answer 4

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