mongooseでschemaをネストする

queries.coffee

Schema   = mongoose.Schema
ObjectId = Schema.ObjectId

# スキーマ定義
PostSchema = new Schema
  title:    type: String, unique: true
  content:  String
  author:   type: ObjectId, ref: 'users'
  comments: [ type: ObjectId, ref: 'comments' ]
  created:  type: Date, default: new Date.now()

CommentSchema = new Schema
  owner:    String
  content:  String
  created:  type: Date, default: new Date.now()

UserSchema = new Schema
  name:     type: String, unique: true

# modelを登録
Post    = mongoose.model 'posts',    PostSchema
Comment = mongoose.model 'comments', CommentSchema
User    = mongoose.model 'users',    UserSchema


# データを作成する
User.findOne name: "geta6", (err, user) ->
  if !err
    second = new Post
      title: "my second post"
      content: "this is my second post."
      author: user._id
    second.save()

# データを読む
Post.findOne( title: "my first post")
    .populate("author")
    .populate("comments")
    .exec (err, post) ->
      if !err
        console.log post

# データを追加する(commentを追加)
Post.findOne title: "my first post", (err, post) ->
  if !err
    comment = new Comment
      owner:    "anonymous"
      content:  "nice post!!"
    comment.save()
    post.comments.push comment._id
    post.save()