Rethinking many-to-many relationships for MongoDB

Question

I am just starting a new Rails 3 project using Mongoid ORM for MongoDB. There is only one thing that I can’t figure out and interact with so many effectively. Now there are good chances that I may be misplacing this problem, but as far as I know, there are at least two containers in my project that need many-to-many relationships. I would prefer to consider both models as “first class” models and select each with its own container.

This is the easiest way I can structure many-to-many relationships:

// Javascript pseudo modeling
// -------------------- Apps
{ 
  app: {
    _id: "app1",
    name: "A",
    event_ids: ["event1","event2"]
  }
}

{ 
  app: {
    _id: "app2",
    name: "B",
    event_ids: ["event1"]
  }
}

// -------------------- Events

{
  event: {
    _id: "event1",
    name: "Event 1",
  }
}

{
  event: {
    _id: "event2",
    name: "Event 2",
  }
}

, , " ". , , , . post commit/save hooks Event App.event_ids, .

? - - " ", .

Answer 1

Mongoid. , ; . , .

. , - .

class App
  include Mongoid::Document
  field :name

  references_one :account
  references_many :events, :stored_as => :array, :inverse_of => :apps

  validates_presence_of :name
end

---

class Event
  include Mongoid::Document
  field :name, :type => String

  references_one :account

  validates_presence_of :name, :account

  before_destroy :remove_app_associations

  def apps
    App.where(:event_ids => self.id).to_a
  end

  def apps= app_array
    unless app_array.kind_of?(Array)
      app_array = [app_array]
    end
    # disassociate existing apps that are not included in app_array
    disassociate_apps App.where(:event_ids => self.id).excludes(:id => app_array.map(&:id)).to_a
    # find existing app relationship ids
    existing_relationship_ids = App.where(:event_ids => self.id, :only => [:id]).map(&:id)
    # filter out existing relationship ids before making the new relationship to app
    push_apps app_array.reject { |app| existing_relationship_ids.include?(app.id) }
  end

  def push_app app
    unless app.event_ids.include?(self.id)
      app.event_ids << self.id
      app.save!
    end
  end

  def disassociate_app app
    if app.event_ids.include?(self.id)
      app.event_ids -= [self.id]
      app.save!
    end
  end

  def push_apps app_array
    app_array.each { |app| push_app(app) }
  end

  def disassociate_apps app_array
    app_array.each { |app| disassociate_app(app) }
  end

  def remove_app_associations
    disassociate_apps apps
  end

end

Answer 2

, mapreduce , . eventid. collection.event_ids.

eventid, , (). , , . , ?

, MongoDB, , "".