Question

I’m just getting started with MongoDB and Mongoid for Rails and in need of some advice on the right way to design a simple blog database.

I’m currently using the structure below, but I need a way to query all comments written by a given user (the relational db equivalent would be Comment.where('user_id = ?', user_id)).

Is this the right set up, or should I move comments out into their own document, and not embed them in posts (as I would in a relational db schema)?

Appreciate any advice, thanks.

Database Schema

post {
  _id: (object id)
  title: string
  body: string
  user_id: reference
  comments: [
    { _id: (object id), body: string, user_id: reference },
    { _id: (object id), body: string, user_id: reference },
    ...
  ]
}

user {
  _id: (object id)
  name: string
}

In MongoDB, my corresponding models are:

class Post
  include Mongoid::Document
  field :title
  field :body
  embeds_many :comments
  references_one :user
end

class Comment
  include Mongoid::Document
  field :body
  embedded_in :post
  references_one :user
end

class User
  include Mongoid::Document
  field :name
  references_many :posts
end

Answer 1

There’s a great article on Mongodb.org about the various choices for modeling comments.

Check out: http://www.mongodb.org/display/DOCS/MongoDB+Data+Modeling+and+Rails#MongoDBDataModelingandRails-ModelingComments