Should Post and Comment be in Post Aggregate or should they be their aggregates?

Question

Consider a typical blog with Post and Comment objects.

For the demo DDD I created, I (so far) have found that both the Post and Comment objects were suitable for the same aggregate — the Post aggregate. But now I'm not sure.

In my controllers, I find, as expected, that I need to add and remove Comments from Posts . With my current model, I do not track Comment identification around the world (as the Blue Book suggests). You can expect my Comment removal action might look like this:

 public ActionResult DeleteComment(int postID, int commentID) 

Obviously, I need a Post ID to retrieve it from the repository and an identifier for a specific Comment on the Post that I want to delete.

My problem is the body of the DeleteComment( :

Is it possible to go through Post using the request mechanism to get Comment to be deleted? eg:

 var comment = this._postRepo.WithID(postID).Comments .SingleOrDefault(c => c.ID == commentID); this._postRepo.Delete(comment); return RedirectToAction("detail", new { id = postID }); 

.. or should I choose Comment from a repo like this ?:

 var comment = this._postRepo.CommentWithID(commentID) 

.. or:

 var comment = this._postRepo.CommentWithID(postID, commentID) 

The two examples above may seem a little silly since I don't need a Post id if I can track Comment globally. But if I track Comment globally, shouldn't it have its own aggregate, and then is it right when Post and Comment seem to go together?

Answer 1

The question is whether the comment has any meaning outside of message aggregation. IMHO, they are not, so I think that you should not move the comment to your own aggregate.

Answer 2

In my opinion, the comment should be part of Post Aggregate, but the comment must be an entity, bcoz two comments with the same answer are still two separate comments.

If you create a comment as a separate unit, where comment is the root, then the comment will have a repository method, which means that any body can create a comment, but the main idea is that a comment should not be created without its post.Comment is associated with the message.

If you think logically, the comment cannot be changed. This means that when creating a comment, it must be part of the message.

Answer 3

As others have said, it depends a lot on whether the comment has any meaning outside the Mail. I tend to think that this happens for several reasons. Firstly, things other than posts can be conceptually commented on in a regular blog (e.g., image, news, other comment). Secondly, as was shown, you often see widgets only comments that are not dependent on their posts. I also think that this scenario makes decisions that you torment more trivially.

However, if you decide to make them a single aggregate, remember that the repository often loads the entire aggregate when executing queries, relying on mechanisms such as caching, etc., to make it effective. Thus, your script will be a request for publication, followed by a search for these comments for comments “correct” for editing / deleting / independently.