dm_save_parents.rb

# I want to be able to check the validity of the parent object
# before saving, and maybe modify it, but I can't use 'before :save'
# because those hooks only run if save_parents is true
#
# I would prefer to not use save_parents because it is part of 
# the private api, but this seems to be the best solution
# I've yet to come across.
#
require 'rubygems'
gem 'dm-core','= 0.10.1'
gem 'dm-validations','= 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 :save_parents do
    return if parent && parent.valid?
    
    self.parent = Parent.new unless parent
    if suffix && suffix == "Jr."
      parent.first_name=first_name
    end
    parent.last_name=last_name
  end
end

DataMapper.auto_migrate!

bill = Child.new :first_name=>'Bill',:last_name=>'William',:suffix=>'Jr.'

puts "save successful: #{bill.save}"
puts "errors empty?: #{bill.errors.empty?}"
puts "parent valid: #{ bill.parent.valid?}"