generated models with

  $ r g active_record:model todo title:string done:boolean
  $ r g model todo_log title:string done:boolean

and add schema options: :null, :default

app/models/todo.rb

@@ -0,0 +1,2 @@
+class Todo < ActiveRecord::Base
+end

app/models/todo_log.rb

@@ -0,0 +1,5 @@
+class TodoLog
+  include Mongoid::Document
+  field :title, :type => String
+  field :done, :type => Boolean
+end

db/migrate/20110730071022_create_todos.rb

@@ -0,0 +1,14 @@
+class CreateTodos < ActiveRecord::Migration
+  def self.up
+    create_table :todos do |t|
+      t.string :title,  :null => false
+      t.boolean :done,  :null => false, :default => false
+
+      t.timestamps
+    end
+  end
+
+  def self.down
+    drop_table :todos
+  end
+end

db/schema.rb

@@ -0,0 +1,22 @@
+# This file is auto-generated from the current state of the database. Instead
+# of editing this file, please use the migrations feature of Active Record to
+# incrementally modify your database, and then regenerate this schema definition.
+#
+# Note that this schema.rb definition is the authoritative source for your
+# database schema. If you need to create the application database on another
+# system, you should be using db:schema:load, not running all the migrations
+# from scratch. The latter is a flawed and unsustainable approach (the more migrations
+# you'll amass, the slower it'll run and the greater likelihood for issues).
+#
+# It's strongly recommended to check this file into your version control system.
+
+ActiveRecord::Schema.define(:version => 20110730071022) do
+
+  create_table "todos", :force => true do |t|
+    t.string   "title",                         :null => false
+    t.boolean  "done",       :default => false, :null => false
+    t.datetime "created_at"
+    t.datetime "updated_at"
+  end
+
+end