Moving document between collections in Mongo (via Mongoid)

Question

I'm building a card game (basic 52 card deck of playing cards 4 suits * 13 ranks), and I've decided on MongoDB for this project.

My basic model is: --> Game --> Deck --> Cards --> Players --> Hand (as Deck) --> Cards --> Final (as Deck) --> Cards --> Closing (as Deck) --> Cards

Ideally I'd like to shift cards off the game's deck into the various piles that Players have.

However, doing something like: game.players[0].hand.cards.push(game.deck.cards.shift(1)) doesn't work, the card in question isn't removed from the game's deck (because #delete is never called), and it isn't added to the player's hand (from my limited understanding, Mongoid will only add new objects to an embedded collection.)

So to move a card from one pile to another, I basically have to do this: game = Game.first player = game.players.first

card = game.deck.cards.shift
copy = Card.new(card.card_id) #read,create
player.hand.cards << copy
if player.save!
  card.delete #delete
  game.save
end

Not earth shatteringly difficult, but I'm basically doing a READ, a DESTROY and a CREATE, to basically emulate what could be a very simple UPDATE.

Is there something I'm missing? Is this a limitation of the Mongoid ODM? Is moving documents between collections a huge no-no?

I'm very open to suggestions about the model, as I have no idea if embedded documents are even a good fit for this type of problem.

Below is the corresponding boiler plate

class Deck
  include Mongoid::Document

  field :is_deck, :type => Boolean



  embedded_in :game
  embedded_in :player
  embeds_many :cards
end

class Card
  include PlayingCards
  include Mongoid::Document

  embedded_in :deck

  field :card_id, :type => Integer
  field :idx, :type => Integer #used to maintain shuffled order since mongodb is insertion order
  field :rank, :type => String
  field :suit, :type => String
end


class Game
  include Mongoid::Document

  embeds_one :deck #deck players draw from
  embeds_many :players

  field :current_player, type: Integer
  field :num_players, type: Integer
end

class Player
  include Mongoid::Document
  embedded_in :game

  embeds_one :hand, class_name: "Deck"
  embeds_one :closing, class_name: "Deck"
  embeds_one :final, class_name: "Deck"
end

Thanks in advance!

score 0 · Answer 1 · answered Sep 20 '11 at 16:51

You should read about difference between embedded and referenced associations.

for ex.

class Parent
  embeds_one :child
end

class Child
  embedded_in :parent
end

Object child = Child.new cant't be created It can be only access via Parent and created on that lavel or destroy.

So you need think what you want to achive if you want to move achieve.

  embedded_in :game
  embedded_in :player

So this already wrong. That should be referenced by (if I correctly understood idea). You cant embed 1 object in 2 documents. This not for embedded is used to.

http://mongoid.org/docs/relations/embedded.html http://mongoid.org/docs/relations/referenced.html

Read this.

Moving document between collections in Mongo (via Mongoid)

1 Answers1