Nosql数据库设计-MongoDB

我正在尝试构建一个只有以下3种模型的应用程序：

topic (has just a title (max 100 chars.))

comment (has text (may be very long), author_id, topic_id, createdDate)

author (has just a username)

Actually a very simple db structure. A Topic may have many comments, which are created by authors. And an author may have many comments.

I am still trying to figure out the best way of designing the database structure (documents). First I though to put everything to its own schema like above. 3 Documents. But since this is a nosql db, I should actually try to eliminate the needs for a join. And now I am really thinking of putting everything to a single document, which also sounds crazy.

These are my actually queries from ui:

Homepage query: Listing all the topics, which have received the most comments today (will run very often)

Auto suggestion list for search field: Listing all the topics, whose title contains string "X"

Main page of a topic query: Listing all the comments of a topic, with their authors' username.

Since most of my queries need data from at least 2 documents, should I really just use them all together in a single document like this:

Comment (text, username, topic_title, createdDate)

This way I will not need any join, but also save i.e. the title of topics multiple times.. in every comment..

I just could not decide.

I appreciate any help.