gistfile1.rb

class User < ActiveRecord::Base
  
  has_many :product_interests
  has_many :products, :through => :product_interests
  
  has_many :brand_interests
  has_many :brands, :through => :brand_interests

  def deals
    product_interests.collect(&:deals) + brand_interests.collect(&:deals)
  end
end

class Deal < ActiveRecord::Base
  belongs_to :brand
  belongs_to :product

  def interested_users
    brand.users
  end
end

class Product
  has_many :deals
  has_many :product_interests
  has_many :users, :through => :product_interests
end

class Brand
  has_many :deals
  has_many :brand_interests
  has_many :users, :through => :brand_interests
end

class ProductInterest
  belong_to :user
  belongs_to :product
  delegate :deals, :to => :product
end

class BrandInterest
  belong_to :user
  belongs_to :brand
  delegate :deals, :to => :brand
end

@user.deals