Database Design – SQL vs NoSQL for Nested Entities and Calculations

I generally agree with your solution and I would do the same, i.e. create a separate model called Share, even though it looks like a RDBMS-like solution.

But let's step back and review the available options.

First of all, consider the relations of your models. Draw them on a piece of paper and note the type of relations and their associations (belongs to, has one, has many, has many through or has_and_belongs_to_many). Perfect reference for the associations in rails is http://guides.rubyonrails.org/association_basics.html. Take into account that Mongoid also offers embedded_in/embeds_many type of relations.

In your case the relations would be: User (1..N) Boards for owning, User (N..N) Boards for sharing.

The hint to decide whether to use has_many, has_and_belongs_to_many or embeds_many is whether or not the subordinate model represents semantically embedded type of relation and is not connected with other models than its parent. It it is, use embeds_many, otherwise use has_many or has_and_belongs_to_many.

The hint to decide whether to use has_many :through or has_and_belongs_to_many is whether you are going to add more data to a linking model (Share in your case).

has_and_belongs_to_many in mongoid is doing without creation of a linking model, i.e. board_ids would be kept as an array in the User model and user_ids would be kept as an array in the Board model.

The reason to not use HABTM in your case is simple. You have two relations between your User and Board models (sharing and owning), you would have difficulty in figuring out what expression like user.boards means (shared boards or owned boards). I don't know of an easy way to separate these two kinds of relations without use of a third model (Share) as you proposed in comments (using :as, etc.)

You can also manually keep the ids of boards in your user model, like this:

class User
  include Mongoid::Document
  field :name
  key :shared_board_ids, Array, :index => true
  key :owned_board_ids, Array, :index => true

  def shared_boards
    Board.find shared_board_ids
  end
  # ...

end

However, difficulties in this case arise pretty fast. You have to manually destroy all board references from the User model when you destroy a board. If you keep a sharing_user_ids in your Board model, you have redundancy and another set of difficulties.

So, yes, I would recommend creating a separate Share model, as I show below.

class User
  include Mongoid::Document
  field :name
  has_many :shares
  has_many :boards
end

class Board
  include Mongoid::Document  
  field :title
  has_many :shares
  belongs_to :user
end

class Share
  include Mongoid::Document  
  belongs_to :user
  belongs_to :board
end

As of permissions, CanCan is simple, but it is doing just fine. Notice a difference between terms authentication (which checks the authenticity of a user, in other words checks that the user is really who he claims he is - normally using password) and authorization (which checks the rights of the user). Authentication is handled by gems like Authlogic, Warden (and Devise based on Warden), Sorcery. Authorization is handled by Declarative_authorization or CanCan.

After your clarifications on the question, I would go by this logic to list recipeids excluding any recipe with a missing/insufficient ingredient.

SELECT recipeid
FROM recipeingredients RI
WHERE recipeid NOT IN (SELECT RI1.recipeid
                       FROM recipeingredients RI1
                       LEFT OUTER JOIN Ingredients I ON RI1.ingredientsid = I.id
                                                    AND RI1.Requiredquantity <= I.availablequantity
                       WHERE I.id IS NULL
                      )