Daniel Data Model

gistfile1.rb

class Item < ActiveRecord::Base
  has_many :user_group_items
  has_many :user_groups, through: :user_group_items
end

class UserGroup < ActiveRecord::Base
  has_many :user_group_items
  has_many :items, through: :user_group_items
end

class UserGroupItems < ActiveRecord::Base
  belongs_to :user_group
  belongs_to :item
end