title: Saving domain entities changes
body: <p>here's real example that will lead to my question: I have an AddCommentToArticleCommand, which has an ArticleId, comment text and email address. This command:</p>
  
  <ul>
  <li>uses the article repository to get the article (which is the domain entity)</li>
  <li>if  article exists, it calls article.AddComment(commentText, emailAddress), which adds the comment to the article and throws exception when it can't (due to invalid email format, article was closed, comment not filled in or too long etc...)</li>
  <li>but now I don't know what the best way is to save the added comment?</li>
  </ul>
  
  <p>Should I do something like articleRepository.Save(article)? But then, why should I save the article if only a comment was added? Or can I do something like articleRepository.SaveComment(comment), that will only save the comment? Or what approach would you take here?</p>
  
  <p>Thanks!</p>