Creating query(join) or correct the design?
// User, the profile is not complete there will be more fields
var u = {
    name: 'Michael', // Is not unique
    email: 'mo@gmail.com', // Should be also unique
    fbid: '4545454asdadsa'
}

db.user.insert(u);

// User can have 0 to many posts

var p = {
    title: 'Suprise',
    body: 'Well done',
    tags: ['first', 'post', 'english'],
    author: 'mo@gmail.com',
    created: new Date(),
    modified: new Date()
};
db.post.insert(p);

var p = {
    title: 'Weather in Estonia',
    body: 'Always looks bad',
    tags: ['bad', 'weather', 'estonia'],
    author: 'mo@gmail.com',
    created: new Date(),
    modified: new Date()
}
db.post.insert(p);

var p = {
    title: 'Suprise',
    body: 'Well done',
    tags: ['first', 'post', 'english'],
    author: {
        name: 'Michael', // Is not unique
        email: 'mo@gmail.com', // Should be also unique
        fbid: '4545454asdadsa'
    },
    created: new Date(),
    modified: new Date()
};

{
  title: String,
  body: String,
  tags: [String],
  author: {
    name: String,
    email: String,
    fbid: String
  },
  created: Date,
  modified: Date,
  comments: [{
    body: String,
    created: Date,
    modified: Date
  }]
}

{
  name: String,
  email: String,
  fbid: String,
  posts: [{
    title: String,
    body: String,
    tags: [String],
    created: Date,
    modified: Date,
    comments: [{
      body: String,
      created: Date,
      modified: Date
    }]
  }]
}

{
  body: String,
  created: Date,
  modified: Date,
  author: {
    name: String,
    email: String,
    fbid: String
  },
  post: {
    title: String,
    body: String,
    tags: [String],
    created: Date,
    modified: Date
    comments: [{
      body: String,
      created: Date,
      modified: Date
    }]
  }
}