Model attribute contains collection of object

I have main model Page, which is container. The page can have some to-do lists, notes, files and discussions. The idea is to have them in special order.

Page.last.container # [Todolist_obj, Note_obj, File_obj, Note_obj, Discussion_obj, File_obj, File_obj]

So I came to approach to use Mongodb
Or I also thought about using Postgres with hstore, but don't know will it help or not
Or maybe just any database and deserialize all objects when getting page, and serialize objects when saving
Or I can make superclass Item and inherit all containing objects from it using MTI and make Page has many relationship.

So I don't know which way is the best?

or perhaps there is a better way?

Solution

I have used acts_as_list for implementing sortable objects very successfully. Additionally, i would abstract the elements of a page into a separate model, here called PageElement.

I think there is no need to switch to a NoSQL database (although i have nothing against this approach). Here is a rough sketch of what i'm thinking:

class Page < ActiveRecord::Base
  has_many :page_elements, :order => 'position'
  has_many :todo_lists,  :through => :page_elements, :source => :element, :source_type => 'TodoList'
  has_many :notes,       :through => :page_elements, :source => :element, :source_type => 'Note'
  has_many :files,       :through => :page_elements, :source => :element, :source_type => 'File'
  has_many :discussions, :through => :page_elements, :source => :element, :source_type => 'Discussion'
end

class PageElement < ActiveRecord::Base
  belongs_to :page
  belongs_to :element, :polymorphic => true
  acts_as_list :scope => :page
end

class TodoList < ActiveRecord::Base
  has_one :page_element, :as => :element
  has_one :page, :through => :page_elements 
end

class Note < ActiveRecord::Base
  has_one :page_element, :as => :element
  has_one :page, :through => :page_elements 
end

class File < ActiveRecord::Base
  has_one :page_element, :as => :element
  has_one :page, :through => :page_elements 
end

class Discussion < ActiveRecord::Base
  has_one :page_element, :as => :element
  has_one :page, :through => :page_elements 
end