aboutsummaryrefslogblamecommitdiffstats
path: root/railties/doc/guides/creating_plugins/basics.markdown
blob: f59e8728d733310c297d385a852dfc330e90f040 (plain) (tree)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861




























































































































































































































































































































































































































































































































































































































































































































































































































































































                                                                                                                                                                                                                                                                                                                       
Creating Plugin Basics
====================

Pretend for a moment that you are an avid bird watcher.  Your favorite bird is the Yaffle, and you want to create a plugin that allows other developers to share in the Yaffle goodness.

In this tutorial you will learn how to create a plugin that includes:

Core Extensions - extending String:

    # Anywhere
    "hello".squawk # => "squawk! hello! squawk!"

An `acts_as_yaffle` method for Active Record models that adds a "squawk" method:

    class Hickwall < ActiveRecord::Base
      acts_as_yaffle :yaffle_text_field => :last_sang_at
    end

    Hickwall.new.squawk("Hello World")

A view helper that will print out squawking info:

    squawk_info_for(@hickwall)

A generator that creates a migration to add squawk columns to a model:

    script/generate yaffle hickwall

A custom generator command:

    class YaffleGenerator < Rails::Generator::NamedBase
      def manifest
          m.yaffle_definition
        end
      end
    end

A custom route method:

    ActionController::Routing::Routes.draw do |map|
      map.yaffles
    end

In addition you'll learn how to:

* test your plugins
* work with init.rb, how to store model, views, controllers, helpers and even other plugins in your plugins
* create documentation for your plugin.
* write custom rake tasks in your plugin

Create the basic app
---------------------

In this tutorial we will create a basic rails application with 1 resource: bird.  Start out by building the basic rails app:

> The following instructions will work for sqlite3.  For more detailed instructions on how to create a rails app for other databases see the API docs.

    rails plugin_demo
    cd plugin_demo
    script/generate scaffold bird name:string
    rake db:migrate
    script/server

Then navigate to [http://localhost:3000/birds](http://localhost:3000/birds).  Make sure you have a functioning rails app before continuing.

Create the plugin
-----------------------

The built-in Rails plugin generator stubs out a new plugin. Pass the plugin name, either CamelCased or under_scored, as an argument. Pass --with-generator to add an example generator also.

This creates a plugin in vendor/plugins including an init.rb and README as well as standard lib, task, and test directories.

Examples:

    ./script/generate plugin BrowserFilters
    ./script/generate plugin BrowserFilters --with-generator

Later in the plugin we will create a generator, so go ahead and add the --with-generator option now:

    script/generate plugin yaffle --with-generator

You should see the following output:

    create  vendor/plugins/yaffle/lib
    create  vendor/plugins/yaffle/tasks
    create  vendor/plugins/yaffle/test
    create  vendor/plugins/yaffle/README
    create  vendor/plugins/yaffle/MIT-LICENSE
    create  vendor/plugins/yaffle/Rakefile
    create  vendor/plugins/yaffle/init.rb
    create  vendor/plugins/yaffle/install.rb
    create  vendor/plugins/yaffle/uninstall.rb
    create  vendor/plugins/yaffle/lib/yaffle.rb
    create  vendor/plugins/yaffle/tasks/yaffle_tasks.rake
    create  vendor/plugins/yaffle/test/core_ext_test.rb
    create  vendor/plugins/yaffle/generators
    create  vendor/plugins/yaffle/generators/yaffle
    create  vendor/plugins/yaffle/generators/yaffle/templates
    create  vendor/plugins/yaffle/generators/yaffle/yaffle_generator.rb
    create  vendor/plugins/yaffle/generators/yaffle/USAGE

For this plugin you won't need the file vendor/plugins/yaffle/lib/yaffle.rb so you can delete that.

    rm vendor/plugins/yaffle/lib/yaffle.rb

> Editor's note:  many plugin authors prefer to keep this file, and add all of the require statements in it.  That way, they only line in init.rb would be `require "yaffle"`
> If you are developing a plugin that has a lot of files in the lib directory, you may want to create a subdirectory like lib/yaffle and store your files in there.  That way your init.rb file stays clean

Setup the plugin for testing
------------------------

Testing plugins that use the entire Rails stack can be complex, and the generator doesn't offer any help.  In this tutorial you will learn how to test your plugin against multiple different adapters using ActiveRecord.  This tutorial will not cover how to use fixtures in plugin tests.

To setup your plugin to allow for easy testing you'll need to add 3 files:

* A database.yml file with all of your connection strings
* A schema.rb file with your table definitions
* A test helper that sets up the database before your tests

For this plugin you'll need 2 tables/models, Hickwalls and Wickwalls, so add the following files:

    # File: vendor/plugins/yaffle/test/database.yml

    sqlite:
      :adapter: sqlite
      :dbfile: yaffle_plugin.sqlite.db
    sqlite3:
      :adapter: sqlite3
      :dbfile: yaffle_plugin.sqlite3.db
    postgresql:
      :adapter: postgresql
      :username: postgres
      :password: postgres
      :database: yaffle_plugin_test
      :min_messages: ERROR
    mysql:
      :adapter: mysql
      :host: localhost
      :username: rails
      :password:
      :database: yaffle_plugin_test

    # File: vendor/plugins/yaffle/test/test_helper.rb

    ActiveRecord::Schema.define(:version => 0) do
      create_table :hickwalls, :force => true do |t|
        t.string :name
        t.string :last_squawk
        t.datetime :last_squawked_at
      end
      create_table :wickwalls, :force => true do |t|
        t.string :name
        t.string :last_tweet
        t.datetime :last_tweeted_at
      end
    end

    # File: vendor/plugins/yaffle/test/test_helper.rb

    ENV['RAILS_ENV'] = 'test'
    ENV['RAILS_ROOT'] ||= File.dirname(__FILE__) + '/../../../..'

    require 'test/unit'
    require File.expand_path(File.join(ENV['RAILS_ROOT'], 'config/environment.rb'))

    config = YAML::load(IO.read(File.dirname(__FILE__) + '/database.yml'))
    ActiveRecord::Base.logger = Logger.new(File.dirname(__FILE__) + "/debug.log")

    db_adapter = ENV['DB']

    # no db passed, try one of these fine config-free DBs before bombing.
    db_adapter ||=
      begin
        require 'rubygems'
        require 'sqlite'
        'sqlite'
      rescue MissingSourceFile
        begin
          require 'sqlite3'
          'sqlite3'
        rescue MissingSourceFile
        end
      end

    if db_adapter.nil?
      raise "No DB Adapter selected. Pass the DB= option to pick one, or install Sqlite or Sqlite3."
    end

    ActiveRecord::Base.establish_connection(config[db_adapter])

    load(File.dirname(__FILE__) + "/schema.rb")

    require File.dirname(__FILE__) + '/../init.rb'

    class Hickwall < ActiveRecord::Base
      acts_as_yaffle
    end

    class Wickwall < ActiveRecord::Base
      acts_as_yaffle :yaffle_text_field => :last_tweet, :yaffle_date_field => :last_tweeted_at
    end

Add a `to_squawk` method to String
-----------------------

To update a core class you will have to:

* Write tests for the desired functionality
* Create a file for the code you wish to use
* Require that file from your init.rb

Most plugins store their code classes in the plugin's lib directory.  When you add a file to the lib directory, you must also require that file from init.rb.  The file you are going to add for this tutorial is `lib/core_ext.rb`

First, you need to write the tests.  Testing plugins is very similar to testing rails apps.  The generated test file should look something like this:

    # File: vendor/plugins/yaffle/test/core_ext_test.rb

    require 'test/unit'

    class CoreExtTest < Test::Unit::TestCase
      # Replace this with your real tests.
      def test_this_plugin
        flunk
      end
    end

Start off by removing the default test, and adding a require statement for your test helper.

    # File: vendor/plugins/yaffle/test/core_ext_test.rb

    require 'test/unit'
    require File.dirname(__FILE__) + '/test_helper.rb'

    class CoreExtTest < Test::Unit::TestCase
    end

Navigate to your plugin directory and run `rake test`

    cd vendor/plugins/yaffle
    rake test

Your test should fail with `no such file to load -- ./test/../lib/core_ext.rb (LoadError)` because we haven't created any file yet.  Create the file `lib/core_ext.rb` and re-run the tests.  You should see a different error message:

    1.) Failure ...
    No tests were specified

Great - now you are ready to start development.  The first thing we'll do is to add a method to String called `to_squawk` which will prefix the string with the word "squawk! ".  The test will look something like this:

    # File: vendor/plugins/yaffle/init.rb

    class CoreExtTest < Test::Unit::TestCase
      def test_string_should_respond_to_squawk
        assert_equal true, "".respond_to?(:to_squawk)
      end
      def test_string_prepend_empty_strings_with_the_word_squawk
        assert_equal "squawk!", "".to_squawk
      end
      def test_string_prepend_non_empty_strings_with_the_word_squawk
        assert_equal "squawk! Hello World", "Hello World".to_squawk
      end
    end

    # File: vendor/plugins/yaffle/init.rb

    require "core_ext"

    # File: vendor/plugins/yaffle/lib/core_ext.rb

    String.class_eval do
      def to_squawk
        "squawk! #{self}".strip
      end
    end

When monkey-patching existing classes it's often better to use `class_eval` instead of opening the class directly.

To test that your method does what it says it does, run the unit tests.  To test this manually, fire up a console and start squawking:

    script/console
    >> "Hello World".to_squawk
    => "squawk! Hello World"

If that worked, congratulations!  You just created your first test-driven plugin that extends a core ruby class.

Add an `acts_as_yaffle` method to ActiveRecord
-----------------------

A common pattern in plugins is to add a method called `acts_as_something` to models.  In this case, you want to write a method called `acts_as_yaffle` that adds a squawk method to your models.

To keep things clean, create a new test file called `acts_as_yaffle_test.rb` in your plugin's test directory and require your test helper.

    # File: vendor/plugins/yaffle/test/acts_as_yaffle_test.rb

    require File.dirname(__FILE__) + '/test_helper.rb'

    class Hickwall < ActiveRecord::Base
      acts_as_yaffle
    end

    class ActsAsYaffleTest < Test::Unit::TestCase
    end

    # File: vendor/plugins/lib/acts_as_yaffle.rb

    module Yaffle
    end

One of the most common plugin patterns for `acts_as_yaffle` plugins is to structure your file like so:

    module Yaffle
      def self.included(base)
        base.send :extend, ClassMethods
      end

      module ClassMethods
        # any method placed here will apply to classes, like Hickwall
        def acts_as_something
          send :include, InstanceMethods
        end
      end

      module InstanceMethods
        # any method placed here will apply to instaces, like @hickwall
      end
    end

With structure you can easily separate the methods that will be used for the class (like `Hickwall.some_method`) and the instance (like `@hickwell.some_method`).

Let's add class method named `acts_as_yaffle` - testing it out first.  You already defined the ActiveRecord models in your test helper, so if you run tests now they will fail.

Back in your `acts_as_yaffle` file, update ClassMethods like so:

    module ClassMethods
      def acts_as_yaffle(options = {})
        send :include, InstanceMethods
      end
    end

Now that test should pass.  Since your plugin is going to work with field names, you need to allow people to define the field names, in case there is a naming conflict.  You can write a few simple tests for this:

    # File: vendor/plugins/yaffle/test/acts_as_yaffle_test.rb

    require File.dirname(__FILE__) + '/test_helper.rb'

    class ActsAsYaffleTest < Test::Unit::TestCase
      def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
        assert_equal "last_squawk", Hickwall.yaffle_text_field
      end
      def test_a_hickwalls_yaffle_date_field_should_be_last_squawked_at
        assert_equal "last_squawked_at", Hickwall.yaffle_date_field
      end
      def test_a_wickwalls_yaffle_text_field_should_be_last_tweet
        assert_equal "last_tweet", Wickwall.yaffle_text_field
      end
      def test_a_wickwalls_yaffle_date_field_should_be_last_tweeted_at
        assert_equal "last_tweeted_at", Wickwall.yaffle_date_field
      end
    end

To make these tests pass, you could modify your `acts_as_yaffle` file like so:

    # File: vendor/plugins/yaffle/lib/acts_as_yaffle.rb

    module Yaffle
      def self.included(base)
        base.send :extend, ClassMethods
      end

      module ClassMethods
        def acts_as_yaffle(options = {})
          cattr_accessor :yaffle_text_field, :yaffle_date_field
          self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
          self.yaffle_date_field = (options[:yaffle_date_field] || :last_squawked_at).to_s
          send :include, InstanceMethods
        end
      end

      module InstanceMethods
      end
    end

Now you can add tests for the instance methods, and the instance method itself:

    # File: vendor/plugins/yaffle/test/acts_as_yaffle_test.rb

    require File.dirname(__FILE__) + '/test_helper.rb'

    class ActsAsYaffleTest < Test::Unit::TestCase

      def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
        assert_equal "last_squawk", Hickwall.yaffle_text_field
      end
      def test_a_hickwalls_yaffle_date_field_should_be_last_squawked_at
        assert_equal "last_squawked_at", Hickwall.yaffle_date_field
      end

      def test_a_wickwalls_yaffle_text_field_should_be_last_squawk
        assert_equal "last_tweet", Wickwall.yaffle_text_field
      end
      def test_a_wickwalls_yaffle_date_field_should_be_last_squawked_at
        assert_equal "last_tweeted_at", Wickwall.yaffle_date_field
      end

      def test_hickwalls_squawk_should_populate_last_squawk
        hickwall = Hickwall.new
        hickwall.squawk("Hello World")
        assert_equal "squawk! Hello World", hickwall.last_squawk
      end
      def test_hickwalls_squawk_should_populate_last_squawked_at
        hickwall = Hickwall.new
        hickwall.squawk("Hello World")
        assert_equal Date.today, hickwall.last_squawked_at
      end

      def test_wickwalls_squawk_should_populate_last_tweet
        wickwall = Wickwall.new
        wickwall.squawk("Hello World")
        assert_equal "squawk! Hello World", wickwall.last_tweet
      end
      def test_wickwalls_squawk_should_populate_last_tweeted_at
        wickwall = Wickwall.new
        wickwall.squawk("Hello World")
        assert_equal Date.today, wickwall.last_tweeted_at
      end
    end

    # File: vendor/plugins/yaffle/lib/acts_as_yaffle.rb

    module Yaffle
      def self.included(base)
        base.send :extend, ClassMethods
      end

      module ClassMethods
        def acts_as_yaffle(options = {})
          cattr_accessor :yaffle_text_field, :yaffle_date_field
          self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
          self.yaffle_date_field = (options[:yaffle_date_field] || :last_squawked_at).to_s
          send :include, InstanceMethods
        end
      end

      module InstanceMethods
        def squawk(string)
          write_attribute(self.class.yaffle_text_field, string.to_squawk)
          write_attribute(self.class.yaffle_date_field, Date.today)
        end
      end
    end

Note the use of write_attribute to write to the field in model.

Create a view helper
-----------------------

Creating a view helper is a 3-step process:

* Add an appropriately named file to the lib directory
* Require the file and hooks in init.rb
* Write the tests

First, create the test to define the functionality you want:

    # File: vendor/plugins/yaffle/test/view_helpers_test.rb

    require File.dirname(__FILE__) + '/test_helper.rb'
    include YaffleViewHelper

    class ViewHelpersTest < Test::Unit::TestCase
      def test_squawk_info_for_should_return_the_text_and_date
        time = Time.now
        hickwall = Hickwall.new
        hickwall.last_squawk = "Hello World"
        hickwall.last_squawked_at = time
        assert_equal "Hello World, #{time.to_s}", squawk_info_for(hickwall)
      end
    end

Then add the following statements to init.rb:

    # File: vendor/plugins/yaffle/init.rb

    require "view_helpers"
    ActionView::Base.send :include, YaffleViewHelper

Then add the view helpers file and

    # File: vendor/plugins/yaffle/lib/view_helpers.rb

    module YaffleViewHelper
      def squawk_info_for(yaffle)
        returning "" do |result|
          result << yaffle.read_attribute(yaffle.class.yaffle_text_field)
          result << ", "
          result << yaffle.read_attribute(yaffle.class.yaffle_date_field).to_s
        end
      end
    end

You can also test this in script/console by using the "helper" method:

    script/console
    >> helper.squawk_info_for(@some_yaffle_instance)

Create a migration generator
-----------------------

When you created the plugin above, you specified the --with-generator option, so you already have the generator stubs in your plugin.

We'll be relying on the built-in rails generate template for this tutorial.  Going into the details of generators is beyond the scope of this tutorial.

Type:

    script/generate

You should see the line:

    Plugins (vendor/plugins): yaffle

When you run `script/generate yaffle` you should see the contents of your USAGE file.  For this plugin, the USAGE file looks like this:

    Description:
        Creates a migration that adds yaffle squawk fields to the given model

    Example:
        ./script/generate yaffle hickwall

        This will create:
            db/migrate/TIMESTAMP_add_yaffle_fields_to_hickwall

Now you can add code to your generator:

    # File: vendor/plugins/yaffle/generators/yaffle/yaffle_generator.rb

    class YaffleGenerator < Rails::Generator::NamedBase
      def manifest
        record do |m|
          m.migration_template 'migration:migration.rb', "db/migrate", {:assigns => yaffle_local_assigns,
            :migration_file_name => "add_yaffle_fields_to_#{custom_file_name}"
          }
        end
      end

      private
        def custom_file_name
          custom_name = class_name.underscore.downcase
          custom_name = custom_name.pluralize if ActiveRecord::Base.pluralize_table_names
        end

        def yaffle_local_assigns
          returning(assigns = {}) do
            assigns[:migration_action] = "add"
            assigns[:class_name] = "add_yaffle_fields_to_#{custom_file_name}"
            assigns[:table_name] = custom_file_name
            assigns[:attributes] = [Rails::Generator::GeneratedAttribute.new("last_squawk", "string")]
            assigns[:attributes] << Rails::Generator::GeneratedAttribute.new("last_squawked_at", "datetime")
          end
        end
    end

Note that you need to be aware of whether or not table names are pluralized.

This does a few things:

* Reuses the built in rails migration_template method
* Reuses the built-in rails migration template

When you run the generator like

    script/generate yaffle bird

You will see a new file:

    # File: db/migrate/20080529225649_add_yaffle_fields_to_birds.rb

    class AddYaffleFieldsToBirds < ActiveRecord::Migration
      def self.up
        add_column :birds, :last_squawk, :string
        add_column :birds, :last_squawked_at, :datetime
      end

      def self.down
        remove_column :birds, :last_squawked_at
        remove_column :birds, :last_squawk
      end
    end

Add a custom generator command
------------------------

You may have noticed above that you can used one of the built-in rails migration commands `m.migration_template`.  You can create your own commands for these, using the following steps:

1. Add the require and hook statements to init.rb
2. Create the commands - creating 3 sets, Create, Destroy, List
3. Add the method to your generator

Working with the internals of generators is beyond the scope of this tutorial, but here is a basic example:

    # File: vendor/plugins/yaffle/init.rb

    require "commands"
    Rails::Generator::Commands::Create.send   :include,  Yaffle::Generator::Commands::Create
    Rails::Generator::Commands::Destroy.send  :include,  Yaffle::Generator::Commands::Destroy
    Rails::Generator::Commands::List.send     :include,  Yaffle::Generator::Commands::List

    # File: vendor/plugins/yaffle/lib/commands.rb

    require 'rails_generator'
    require 'rails_generator/commands'

    module Yaffle #:nodoc:
      module Generator #:nodoc:
        module Commands #:nodoc:
          module Create
            def yaffle_definition
              file("definition.txt", "definition.txt")
            end
          end

          module Destroy
            def yaffle_definition
              file("definition.txt", "definition.txt")
            end
          end

          module List
            def yaffle_definition
              file("definition.txt", "definition.txt")
            end
          end
        end
      end
    end

    # File: vendor/plugins/yaffle/generators/yaffle/templates/definition.txt

    Yaffle is a bird

    # File: vendor/plugins/yaffle/generators/yaffle/yaffle_generator.rb

    class YaffleGenerator < Rails::Generator::NamedBase
      def manifest
          m.yaffle_definition
        end
      end
    end

This example just uses the built-in "file" method, but you could do anything that ruby allows.

Add a Custom Route
------------------------

Testing routes in plugins can be complex, especially if the controllers are also in the plugin itself.  Jamis Buck showed a great example of this in [http://weblog.jamisbuck.org/2006/10/26/monkey-patching-rails-extending-routes-2](http://weblog.jamisbuck.org/2006/10/26/monkey-patching-rails-extending-routes-2)

    # File: vendor/plugins/yaffle/test/routing_test.rb

    require "#{File.dirname(__FILE__)}/test_helper"

    class RoutingTest < Test::Unit::TestCase

      def setup
        ActionController::Routing::Routes.draw do |map|
          map.yaffles
        end
      end

      def test_yaffles_route
        assert_recognition :get, "/yaffles", :controller => "yaffles_controller", :action => "index"
      end

      private

        # yes, I know about assert_recognizes, but it has proven problematic to
        # use in these tests, since it uses RouteSet#recognize (which actually
        # tries to instantiate the controller) and because it uses an awkward
        # parameter order.
        def assert_recognition(method, path, options)
          result = ActionController::Routing::Routes.recognize_path(path, :method => method)
          assert_equal options, result
        end
    end

    # File: vendor/plugins/yaffle/init.rb

    require "routing"
    ActionController::Routing::RouteSet::Mapper.send :include, Yaffle::Routing::MapperExtensions

    # File: vendor/plugins/yaffle/lib/routing.rb

    module Yaffle #:nodoc:
      module Routing #:nodoc:
        module MapperExtensions
          def yaffles
            @set.add_route("/yaffles", {:controller => "yaffles_controller", :action => "index"})
          end
        end
      end
    end

    # File: config/routes.rb

    ActionController::Routing::Routes.draw do |map|
      ...
      map.yaffles
    end

You can also see if your routes work by running `rake routes` from your app directory.

Generate RDoc Documentation
-----------------------

Once your plugin is stable, the tests pass on all database and you are ready to deploy do everyone else a favor and document it!  Luckily, writing documentation for your plugin is easy.

The first step is to update the README file with detailed information about how to use your plugin.  A few key things to include are:

* Your name
* How to install
* How to add the functionality to the app (several examples of common use cases)
* Warning, gotchas or tips that might help save users time

Once your README is solid, go through and add rdoc comments to all of the methods that developers will use.

Before you generate your documentation, be sure to go through and add nodoc comments to those modules and methods that are not important to your users.

Once your comments are good to go, navigate to your plugin directory and run

    rake rdoc

Work with init.rb
------------------------

The plugin initializer script init.rb is invoked via `eval` (not require) so it has slightly different behavior.

If you reopen any classes in init.rb itself your changes will potentially be made to the wrong module.  There are 2 ways around this:

The first way is to explicitly define the top-level module space for all modules and classes, like ::Hash

    # File: vendor/plugins/yaffle/init.rb

    class ::Hash
      def is_a_special_hash?
        true
      end
    end

OR you can use `module_eval` or `class_eval`

    # File: vendor/plugins/yaffle/init.rb

    Hash.class_eval do
      def is_a_special_hash?
        true
      end
    end

Store models, views, helpers, and controllers in your plugins
------------------------

You can easily store models, views, helpers and controllers in plugins.  Just create a folder for each in the lib folder, add them to the load path and remove them from the load once path:

    # File: vendor/plugins/yaffle/init.rb

    %w{ models controllers helpers }.each do |dir|
      path = File.join(directory, 'lib', dir)
      $LOAD_PATH << path
      Dependencies.load_paths << path
      Dependencies.load_once_paths.delete(path)
    end

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.

Adding directories to the load once paths allow those changes to picked up as soon as you save the file - without having to restart the web server.

Write custom rake tasks in your plugin
-------------------------

When you created the plugin with the built-in rails generator, it generated a rake file for you in `vendor/plugins/yaffle/tasks/yaffle.rake`.  Any rake task you add here will be available to the app.

Many plugin authors put all of their rake tasks into a common namespace that is the same as the plugin, like so:

    # File: vendor/plugins/yaffle/tasks/yaffle.rake

    namespace :yaffle do
      desc "Prints out the word 'Yaffle'"
      task :squawk => :environment do
        puts "squawk!"
      end
    end

When you run `rake -T` from your plugin you will see

  yaffle:squawk "Prints out..."

You can add as many files as you want in the tasks directory, and if they end in .rake Rails will pick them up.

Store plugins in alternate locations
-------------------------

You can store plugins wherever you want - you just have to add those plugins to the plugins path in environment.rb

Since the plugin is only loaded after the plugin paths are defined, you can't redefine this in your plugins - but it may be good to now.

You can even store plugins inside of other plugins for complete plugin madness!

    config.plugin_paths << File.join(RAILS_ROOT,"vendor","plugins","yaffle","lib","plugins")

Create your own Plugin Loaders and Plugin Locators
------------------------

If the built-in plugin behavior is inadequate, you can change almost every aspect of the location and loading process.  You can write your own plugin locators and plugin loaders, but that's beyond the scope of this tutorial.

Use Custom Plugin Generators
------------------------

If you are an RSpec fan, you can install the `rspec_plugin_generator`, which will generate the spec folder and database for you.

[http://github.com/pat-maddox/rspec-plugin-generator/tree/master](http://github.com/pat-maddox/rspec-plugin-generator/tree/master)

References
------------------------

* [http://nubyonrails.com/articles/the-complete-guide-to-rails-plugins-part-i](http://nubyonrails.com/articles/the-complete-guide-to-rails-plugins-part-i)
* [http://nubyonrails.com/articles/2006/05/09/the-complete-guide-to-rails-plugins-part-ii](http://nubyonrails.com/articles/2006/05/09/the-complete-guide-to-rails-plugins-part-ii)
* [http://github.com/technoweenie/attachment_fu/tree/master](http://github.com/technoweenie/attachment_fu/tree/master)
* [http://daddy.platte.name/2007/05/rails-plugins-keep-initrb-thin.html](http://daddy.platte.name/2007/05/rails-plugins-keep-initrb-thin.html)

Appendices
------------------------

The final plugin should have a directory structure that looks something like this:

    |-- MIT-LICENSE
    |-- README
    |-- Rakefile
    |-- generators
    |   `-- yaffle
    |       |-- USAGE
    |       |-- templates
    |       |   `-- definition.txt
    |       `-- yaffle_generator.rb
    |-- init.rb
    |-- install.rb
    |-- lib
    |   |-- acts_as_yaffle.rb
    |   |-- commands.rb
    |   |-- core_ext.rb
    |   |-- routing.rb
    |   `-- view_helpers.rb
    |-- tasks
    |   `-- yaffle_tasks.rake
    |-- test
    |   |-- acts_as_yaffle_test.rb
    |   |-- core_ext_test.rb
    |   |-- database.yml
    |   |-- debug.log
    |   |-- routing_test.rb
    |   |-- schema.rb
    |   |-- test_helper.rb
    |   `-- view_helpers_test.rb
    |-- uninstall.rb
    `-- yaffle_plugin.sqlite3.db