vendor/rails/railties/doc/guides/source/creating_plugins/models.txt

   1 == Add a model ==
   2
   3 This section describes how to add a model named 'Woodpecker' to your plugin that will behave the same as a model in your main app.  When storing models, controllers, views and helpers in your plugin, it's customary to keep them in directories that match the rails directories.  For this example, create a file structure like this:
   4
   5 ---------------------------------------------------------
   6 vendor/plugins/yaffle/
   7 |-- lib
   8 |   |-- app
   9 |   |   |-- controllers
  10 |   |   |-- helpers
  11 |   |   |-- models
  12 |   |   |   `-- woodpecker.rb
  13 |   |   `-- views
  14 |   |-- yaffle
  15 |   |   |-- acts_as_yaffle.rb
  16 |   |   |-- commands.rb
  17 |   |   `-- core_ext.rb
  18 |   `-- yaffle.rb
  19 ---------------------------------------------------------
  20
  21 As always, start with a test:
  22
  23 *vendor/plugins/yaffle/yaffle/woodpecker_test.rb:*
  24
  25 [source, ruby]
  26 ----------------------------------------------
  27 require File.dirname(__FILE__) + '/test_helper.rb'
  28
  29 class WoodpeckerTest < Test::Unit::TestCase
  30   load_schema
  31
  32   def test_woodpecker
  33     assert_kind_of Woodpecker, Woodpecker.new
  34   end
  35 end
  36 ----------------------------------------------
  37
  38 This is just a simple test to make sure the class is being loaded correctly.  After watching it fail with `rake`, you can make it pass like so:
  39
  40 *vendor/plugins/yaffle/lib/yaffle.rb:*
  41
  42 [source, ruby]
  43 ----------------------------------------------
  44 %w{ models }.each do |dir|
  45   path = File.join(File.dirname(__FILE__), 'app', dir)
  46   $LOAD_PATH << path
  47   ActiveSupport::Dependencies.load_paths << path
  48   ActiveSupport::Dependencies.load_once_paths.delete(path)
  49 end
  50 ----------------------------------------------
  51
  52 Adding directories to the load path makes them appear just like files in the the main app directory - except that they are only loaded once, so you have to restart the web server to see the changes in the browser.  Removing directories from the 'load_once_paths' allow those changes to picked up as soon as you save the file - without having to restart the web server.  This is particularly useful as you develop the plugin.
  53
  54
  55 *vendor/plugins/yaffle/lib/app/models/woodpecker.rb:*
  56
  57 [source, ruby]
  58 ----------------------------------------------
  59 class Woodpecker < ActiveRecord::Base
  60 end
  61 ----------------------------------------------
  62
  63 Finally, add the following to your plugin's 'schema.rb':
  64
  65 *vendor/plugins/yaffle/test/schema.rb:*
  66
  67 [source, ruby]
  68 ----------------------------------------------
  69 ActiveRecord::Schema.define(:version => 0) do
  70   create_table :woodpeckers, :force => true do |t|
  71     t.string :name
  72   end
  73 end
  74 ----------------------------------------------
  75
  76 Now your test should be passing, and you should be able to use the Woodpecker model from within your rails app, and any changes made to it are reflected immediately when running in development mode.