class MaterialFeature < ActiveRecord::Base
  has_many  :materials
  has_many  :material_names,    :through=>:materials
end


class MaterialName < ActiveRecord::Base
  has_many  :materials
  has_many  :material_features,   :through=>:materials
end



#essa tabela Material é o resultado do relacionamento N<>N entre as tabelas MaterialFeature e MaterialName
class Material < ActiveRecord::Base
  belongs_to :material_name
  belongs_to :material_feature
end