Relations in Document-oriented database?

Question

I'm interested in document-oriented databases, and I'd like to play with MongoDB. So I started a fairly simple project (an issue tracker), but am having hard times thinking in a non-relational way.

My problems:

1. I have two objects that relate to each other (e.g. issue = {code:"asdf-11", title:"asdf", reporter:{username:"qwer", role:"manager"}} - here I have a user related to the issue). Should I create another document 'user' and reference it in 'issue' document by its id (like in relational databases), or should I leave all the user's data in the subdocument?

2. If I have objects (subdocuments) in a document, can I update them all in a single query?

Answer 1

I'm totally new to document-oriented databases, and right now I'm trying to develop sort of a CMS using node.js and mongodb so I'm facing the same problems as you.

By trial and error I found this rule of thumb: I make a collection for every entity that may be a "subject" for my queries, while embedding the rest inside other objects.

For example, comments in a blog entry can be embedded, because usually they're bound to the entry itself and I can't think about a useful query made globally on all comments. On the other side, tags attached to a post might deserve their own collection, because even if they're bound to the post, you might want to reason globally about all the tags (for example making a list of trending topics).