dm discriminator.rb

require 'rubygems'
require 'dm-core'
require 'dm-migrations'
require 'dm-validations'

class Pet
 include DataMapper::Resource
	
belongs_to :human

 property :id, Serial
 property :name, String, :required => true
 property :type, Discriminator 
end

class Human
 include DataMapper::Resource
 has n, :pets

 property :id, Serial
 property :name, String
end

class Dog < Pet
end


DataMapper.setup(:default, "sqlite3::memory:")
DataMapper.auto_migrate!
DataMapper.finalize

pet = Pet.new
puts pet.valid? # => false
puts pet.errors.inspect # => #<DataMapper::Validations::ValidationErrors:0x10127de48 @errors=#<OrderedHash {:human_id=>["Human must not be blank"], :name=>["Name must not be blank"]}>, @resource=#<Pet @id=nil @name=nil @type=Pet @human_id=nil>>

pet = Pet.new(:name => "timmy")
puts pet.valid? # => false
puts pet.errors.inspect # => #<DataMapper::Validations::ValidationErrors:0x101172558 @errors=#<OrderedHash {:human_id=>["Human must not be blank"]}>, @resource=#<Pet @id=nil @name="timmy" @type=Pet @human_id=nil>>


pet = Pet.new(:name => "timmy", :human => Human.create(:name => "noddy"))
puts pet.valid? # => true

dog = Dog.new
puts dog.valid? # => false
puts dog.errors.inspect # => #<DataMapper::Validations::ValidationErrors:0x1043c7fd0 @errors=#<OrderedHash {:name=>["Name must not be blank"]}>, @resource=#<Dog @id=nil @name=nil @type=Dog @human_id=nil>>

dog = Dog.new(:name => "spot")
puts dog.valid? # => true
puts dog.errors.inspect # => #<DataMapper::Validations::ValidationErrors:0x1044f0308 @errors=#<OrderedHash {}>, @resource=#<Dog @id=nil @name="spot" @type=Dog @human_id=nil>>
puts dog.save # => false