Databases
StackOverflow2013
Postsdbo
POShould Post and Comment be in the Post Aggregate or should they be aggregates of their own?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POShould Post and Comment be in the Post Aggregate or should they be aggregates of their own?
    primarykey
    data
    text
    <p>Consider the typical blog with objects <code>Post</code> and <code>Comment</code>.</p> <p>For a DDD demo example i have been building i have (till now) found that both the entities <code>Post</code> and <code>Comment</code> have been appropriate for the same aggregate- the <code>Post</code> aggregate. But now i'm not so sure..</p> <p>In my controllers i am finding, like you would expect, that i need to add and remove <code>Comments</code> from <code>Posts</code>. With my current model i am not tracking the identity of a <code>Comment</code> globally (like the Blue Book suggests). You you might expect that my action to delete a <code>Comment</code> may look like this:</p> <pre><code>public ActionResult DeleteComment(int postID, int commentID) </code></pre> <p>Obviously i need the <code>Post</code>'s id to retrieve it from the repository and the identifier for the particular <code>Comment</code> on that <code>Post</code> that i want to delete.</p> <p>My problem is the body of the <code>DeleteComment(</code> action:</p> <p>Is it ok to traverse the <code>Post</code> with a query mechanism to get the <code>Comment</code> for deletion? like this:</p> <pre><code>var comment = this._postRepo.WithID(postID).Comments .SingleOrDefault(c =&gt; c.ID == commentID); this._postRepo.Delete(comment); return RedirectToAction("detail", new { id = postID }); </code></pre> <p>..or should i be selecting the <code>Comment</code> from the repo similar to this?:</p> <pre><code>var comment = this._postRepo.CommentWithID(commentID) </code></pre> <p>..or:</p> <pre><code>var comment = this._postRepo.CommentWithID(postID, commentID) </code></pre> <p>The two above examples might seem a little silly since i shouldn't need the <code>Post</code> ID if i can track the <code>Comment</code> globally. But then if i'm tracking the <code>Comment</code> globally, shouldn't it have it's own aggregate and then is that right when <code>Post</code> and <code>Comment</code> seem to go together?</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USMatt Kocaj
    1. USMatt Kocaj
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POShould Post and Comment be in the Post Aggregate or should they be aggregates of their own?
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POShould Post and Comment be in the Post Aggregate or should they be aggregates of their own?
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POShould Post and Comment be in the Post Aggregate or should they be aggregates of their own?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COI think that Post and Comment are different aggregates. You may want to query comments across all posts, for instance. This morning Ayende Rahien (RavenDB author) did a webinar on document databases with the Post/Comment model and he made them separate roots but had a denormalized query for displaying a single post with it's comments. Granted the RavenDB website shows a similar model with everything under Post. I suppose where you put it really depends on what you want to do with the model.
      singulars
      1. POShould Post and Comment be in the Post Aggregate or should they be aggregates of their own?
      1. USRyan
    2. CO@Ryan Agreed. And i'm feeling that it will need to move to separate aggregates. I just want to make sure i'm doing the right thing. And when you say "it really depends on what you want to do with the model" - all im trying to do is the basic AddPost, UpdatePost, DeletePost, AddComment and DeleteComment at this stage - this demo is simplistic so i can understand the DDD decisions involved. "denormalized query for displaying a single post with it's comments": does this mean a way for the Post repo to return Posts and Comments together in an 'aggregated' fashion?
      singulars
      1. POShould Post and Comment be in the Post Aggregate or should they be aggregates of their own?
      1. USMatt Kocaj
    3. COYes it would. You could probably return a view model directly from your service/repo layer that has a post with it's associated comments.
      singulars
      1. POShould Post and Comment be in the Post Aggregate or should they be aggregates of their own?
      1. USRyan
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload