dm_parent_validation_etc.rb

require 'rubygems'
#gem 'dm-core','= 0.10.1'

require 'dm-core'
require 'dm-validations'
DataMapper.setup :default, 'sqlite3::memory:'

class Parent
  include DataMapper::Resource
  property :id,Serial
  property :first_name,String,:nullable=>false
  property :last_name,String,:nullable=>false
  has n, :children
end

class Child
  include DataMapper::Resource
  property :id,Serial
  property :first_name,String,:nullable=>false
  property :last_name,String,:nullable=>false
  property :suffix,String
  
  belongs_to :parent
  
  #before :valid?, :set_jrs_parent
  def set_jrs_parent
    return if parent && parent.valid?
    
    parent = Parent.new unless parent
    if suffix && suffix == "Jr."
      parent.first_name=first_name
    end
    parent.last_name=last_name
    parent.save
    self.parent = parent
  end
  
  
end

DataMapper.auto_migrate!

bill = Child.new :first_name=>'Bill',:last_name=>'William',:suffix=>'Jr.'
bill.parent = Parent.new
puts "save successful: #{bill.save}"
puts "errors empty?: #{bill.errors.empty?}"
puts "parent valid: #{ bill.parent.valid?}"
bill.set_jrs_parent
puts "save after fix?: #{bill.save}"

#---Output--------------
# save successful: false
# errors empty?: true
# parent valid: false
# save after fix?: true