gistfile1.rb

module DataMapper
  module Model::Relationship
    # By default, when validating a model, any child models will not be
    # checked for validation. This means that the following situation can
    # occur:
    #
    #   user = User.new(:author => Author.new)
    #   user.valid?        # => false
    #   user.author.valid? # => false
    #
    # This monkey patch automatically adds a validation to all associations
    # so that both methods in the above example will return false. Validations
    # are only run on dirty models (which includes new models), since clean
    # ones are assumed to be valid.
    def has_with_validation(cardinality, property, *args)
      has_without_validation(cardinality, property, *args)
      case cardinality
      when 1
        validates_with_block property do
          val = send(property)
          if val && val.dirty? && !val.valid?
            [false, "#{property.to_s.titleize} must be valid"]
          else
            true
          end
        end
      when n
        validates_with_block property do
          val = send(property)
          if val.map(&:valid?).all?
            true
          else
            [false, "#{property.to_s.titleize} must be valid"]
          end
        end
      end
    end

     alias_method_chain :has, :validation
  end
end

gistfile2.rb

module DataMapper
  module Resource
    # Wrap a transaction around the save, useful when multiple nested models
    # will be saved at the same time.
    def save_with_transaction(*args)
      ret = nil
      transaction do
        ret = save(*args)
      end
      ret
    end
  end
end