gistfile1.rb

class Project
  include DataMapper::Resource

  property :id,     Serial
  property :title,  String, :nullable => false

  has 2..n, :tasks
  
  def create_or_update 
    transaction do |tnx|
      raise "error with project" unless save
      tasks.each do |t|
        raise "Error with tasks" unless t.save
      end
    end
  end
end

class Task
  include DataMapper::Resource

  property :id,         Serial
  property :project_id, Integer,  :key => true
  property :title,      String,   :nullable => false

  belongs_to :project
end