many_to_many.rb

Class Article < ActiveRecord::Base
  has_many :article_newspapers
  has_many :newspapers, :through => :article_newspapers
end

Class Newspaper < ActiveRecord::Base
  has_many :article_newspapers
  has_many :articles, :through => :article_newspapers
end

Class ArticleNewspaper < ActiveRecord::Base #the join table
  belongs_to :article
  belongs_to :newspaper
end