gistfile1.rb

class Component
  include DataMapper::Resource
  property :id,           Serial
  property :nome,         String
  property :descrizione,  Text
  property :prezzo_base,  Float
  property :base,         Boolean

  has n, :plant_types, :through => Resource

  belongs_to :supplier
  belongs_to :component_type
end

class Supplier
  include DataMapper::Resource

  property :id,               Serial
  property :nome,             String
  property :ragione_sociale,  String
  property :piva,             String
  property :cf,               String

  has n, :components
end

class ComponentType
  include DataMapper::Resource

  property :id,   Serial
  property :nome, String
  property :note, Text

  has n, :components
end

class PlantType
  include DataMapper::Resource

  property :id,   Serial
  property :nome, String #, :required => true, :unique => true

  has n, :components, :through => Resource
end