var CommentSchema = mongoose.Schema({
  body: String,
  created: {
    by: {
      type: String,
      required: true
    },
    date: {
      type: Date,
      default: Date.now
    }
  }
});

var BlogSchema = mongoose.Schema({
  title: String,
  blog: String,
  created: {
    by: {
      type: String,
      required: true
    },
    date: {
      type: Date,
      default: Date.now
    }
  },
  comments: [CommentSchema]
});

var Blog = mongoose.model('Blog', BlogSchema);

Blog.findOne({
  _id: id
}, function(err, blog) {
  console.log(blog); // causes toJSON to be executed
});
// outputs:
{
  title: 'My first blog! #Super',
  blog: 'This is my very first #blog! I hope you enjoy it. #WOOHOO',
  _id: 532cb63e25e4ad524ba17102,
  __v: 0,
  comments: [], // SHOULD THIS BE INCLUDED??
  created: {
    by: 'Joe',
    date: Fri Mar 21 2014 17: 59: 26 GMT - 0400(EDT)
  }
}

Blog.findOne({
  _id: id
}, 'title', function(err, blog) {
  console.log(blog); // causes toJSON to be executed
});
// outputs:
{
  title: 'My first blog! #Super',
  _id: 532caa3841176afb4a7c8476,
  created: {} // SHOULD THIS BE INCLUDED??
}

Blog.findOne({
      _id: id
    }, 'title', function(err, blog) {
      console.log(JSON.parse(JSON.stringify(blog))); // causes toJSON to be executed
    });
     // outputs:
     {
      title: 'My first blog! #Super',
      _id: 532caa3841176afb4a7c8476
    }

Blog.findOne({
      _id: id
    }, function(err, blog) {
      console.log(JSON.parse(JSON.stringify(blog))); // causes toJSON to be executed
    });
     // outputs:
     {
      title: 'My first blog! #Super',
      blog: 'This is my very first #blog! I hope you enjoy it. #WOOHOO',
      _id: 532cb63e25e4ad524ba17102,
      __v: 0,
      comments: [], // SHOULD THIS BE INCLUDED??
      created: {
        by: 'Joe',
        date: Fri Mar 21 2014 17: 59: 26 GMT - 0400(EDT)
      }
    }