aboutsummaryrefslogtreecommitdiffstats
path: root/railties/guides/source/plugins.textile
blob: 79bbe495bd7f7f9fa0be7289efa765c369ad1e6a (plain) (blame)
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
h2. The Basics of Creating Rails Plugins

A Rails plugin is either an extension or a modification of the core framework. Plugins provide:

* a way for developers to share bleeding-edge ideas without hurting the stable code base
* a segmented architecture so that units of code can be fixed or updated on their own release schedule
* an outlet for the core developers so that they don’t have to include every cool new feature under the sun

After reading this guide you should be familiar with:

* Creating a plugin from scratch
* Writing and running tests for the plugin

This guide describes how to build a test-driven plugin that will:

* Extend core ruby classes like Hash and String
* Add methods to ActiveRecord::Base in the tradition of the 'acts_as' plugins
* Give you information about where to put generators in your plugin.

For the purpose of this guide 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.

endprologue.

h3. Setup

Before you continue, take a moment to decide if your new plugin will be potentially shared across different Rails applications.

* If your plugin is specific to your application, your new plugin will be a _vendored plugin_.
* If you think your plugin may be used across applications, build it as a _gemified plugin_.

h4. Either generate a vendored plugin...

Use the +rails generate plugin+ command in your Rails root directory
 to create a new plugin that will live in the +vendor/plugins+
 directory. See usage and options by asking for help:

<shell>
$ rails generate plugin --help
</shell>

h4. Or generate a gemified plugin.

Writing your Rails plugin as a gem, rather than as a vendored plugin,
 lets you share your plugin across different rails applications using
 RubyGems and Bundler.

Rails 3.1 ships with a +rails plugin new+ command which creates a
 skeleton for developing any kind of Rails extension with the ability
 to run integration tests using a dummy Rails application. See usage
 and options by asking for help:

<shell>
$ rails plugin --help
</shell>

h3. Testing your newly generated plugin

You can navigate to the directory that contains the plugin, run the +bundle install+ command
 and run the one generated test using the +rake+ command.

You should see:

<shell>
	2 tests, 2 assertions, 0 failures, 0 errors, 0 skips
</shell>

This will tell you that everything got generated properly and you are ready to start adding functionality.

h3. Extending Core Classes

This section will explain how to add a method to String that will be available anywhere in your rails application.

In this example you will add a method to String named +to_squawk+. To begin, create a new test file with a few assertions:

<ruby>
# yaffle/test/core_ext_test.rb

require 'test_helper'

class CoreExtTest < Test::Unit::TestCase
  def test_to_squawk_prepends_the_word_squawk
    assert_equal "squawk! Hello World", "Hello World".to_squawk
  end
end
</ruby>

Run +rake+ to run the test. This test should fail because we haven't implemented the +to_squak+ method:

<shell>
	  1) Error:
	test_to_squawk_prepends_the_word_squawk(CoreExtTest):
	NoMethodError: undefined method `to_squawk' for "Hello World":String
	    test/core_ext_test.rb:5:in `test_to_squawk_prepends_the_word_squawk'
</shell>

Great - now you are ready to start development.

Then in +lib/yaffle.rb+ require +lib/core_ext+:

<ruby>
# yaffle/lib/yaffle.rb

require "yaffle/core_ext"

module Yaffle
end
</ruby>

Finally, create the +core_ext.rb+ file and add the +to_squawk+ method:

<ruby>
# yaffle/lib/yaffle/core_ext.rb

String.class_eval do
  def to_squawk
    "squawk! #{self}".strip
  end
end
</ruby>

To test that your method does what it says it does, run the unit tests with +rake+ from your plugin directory.

<shell>
	3 tests, 3 assertions, 0 failures, 0 errors, 0 skips
</shell>

To see this in action, change to the test/dummy directory, fire up a console and start squawking:

<shell>
$ rails console
>> "Hello World".to_squawk
=> "squawk! Hello World"
</shell>

h3. Add an "acts_as" Method to Active Record

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 Active Record models.

To begin, set up your files so that you have:

<ruby>
# yaffle/test/acts_as_yaffle_test.rb

require 'test_helper'

class ActsAsYaffleTest < Test::Unit::TestCase
end
</ruby>

<ruby>
# yaffle/lib/yaffle.rb

require "yaffle/core_ext"
require 'yaffle/acts_as_yaffle'

module Yaffle
end
</ruby>

<ruby>
# yaffle/lib/yaffle/acts_as_yaffle.rb

module Yaffle
  module ActsAsYaffle
    # your code will go here
  end
end
</ruby>

h4. Add a Class Method

This plugin will expect that you've added a method to your model named 'last_squawk'. However, the
plugin users might have already defined a method on their model named 'last_squawk' that they use
for something else. This plugin will allow the name to be changed by adding a class method called 'yaffle_text_field'.

To start out, write a failing test that shows the behavior you'd like:

<ruby>
# yaffle/test/acts_as_yaffle_test.rb

require 'test_helper'

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_wickwalls_yaffle_text_field_should_be_last_tweet
    assert_equal "last_tweet", Wickwall.yaffle_text_field
  end

end
</ruby>

When you run +rake+, you should see the following:

<shell>
	  1) Error:
	test_a_hickwalls_yaffle_text_field_should_be_last_squawk(ActsAsYaffleTest):
	NameError: uninitialized constant ActsAsYaffleTest::Hickwall
	    test/acts_as_yaffle_test.rb:6:in `test_a_hickwalls_yaffle_text_field_should_be_last_squawk'

	  2) Error:
	test_a_wickwalls_yaffle_text_field_should_be_last_tweet(ActsAsYaffleTest):
	NameError: uninitialized constant ActsAsYaffleTest::Wickwall
	    test/acts_as_yaffle_test.rb:10:in `test_a_wickwalls_yaffle_text_field_should_be_last_tweet'

	5 tests, 3 assertions, 0 failures, 2 errors, 0 skips
</shell>

This tells us that we don't have the necessary models (Hickwall and Wickwall) that we are trying to test.
We can easily generate these models in our "dummy" Rails application by running the following commands from the
test/dummy directory:

<shell>
$ cd test/dummy
$ rails generate model Hickwall last_squak:string
$ rails generate model Wickwall last_squak:string last_tweet:string
</shell>

Now you can create the necessary database tables in your testing database by navigating to your dummy app
and migrating the database. First

<shell>
$ cd test/dummy
$ rake db:migrate
$ rake db:test:prepare
</shell>

While you are here, change the Hickwall and Wickwall models so that they know that they are supposed to act
like yaffles.

<ruby>
# test/dummy/app/models/hickwall.rb

class Hickwall < ActiveRecord::Base
  acts_as_yaffle
end

# test/dummy/app/models/wickwall.rb

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

</ruby>

We will also add code to define the acts_as_yaffle method.

<ruby>
# yaffle/lib/yaffle/acts_as_yaffle.rb
module Yaffle
  module ActsAsYaffle
    extend ActiveSupport::Concern

    included do
    end

    module ClassMethods
      def acts_as_yaffle(options = {})
        # your code will go here
      end
    end
  end
end

ActiveRecord::Base.send :include, Yaffle::ActsAsYaffle
</ruby>

You can then return to the root directory (+cd ../..+) of your plugin and rerun the tests using +rake+.

<shell>
	  1) Error:
	test_a_hickwalls_yaffle_text_field_should_be_last_squawk(ActsAsYaffleTest):
	NoMethodError: undefined method `yaffle_text_field' for #<Class:0x000001016661b8>
	    /Users/xxx/.rvm/gems/ruby-1.9.2-p136@xxx/gems/activerecord-3.0.3/lib/active_record/base.rb:1008:in `method_missing'
	    test/acts_as_yaffle_test.rb:5:in `test_a_hickwalls_yaffle_text_field_should_be_last_squawk'

	  2) Error:
	test_a_wickwalls_yaffle_text_field_should_be_last_tweet(ActsAsYaffleTest):
	NoMethodError: undefined method `yaffle_text_field' for #<Class:0x00000101653748>
	    Users/xxx/.rvm/gems/ruby-1.9.2-p136@xxx/gems/activerecord-3.0.3/lib/active_record/base.rb:1008:in `method_missing'
	    test/acts_as_yaffle_test.rb:9:in `test_a_wickwalls_yaffle_text_field_should_be_last_tweet'

	5 tests, 3 assertions, 0 failures, 2 errors, 0 skips

</shell>

Getting closer...now we will implement the code of the acts_as_yaffle method to make the tests pass.

<ruby>
# yaffle/lib/yaffle/acts_as_yaffle.rb

module Yaffle
  module ActsAsYaffle
   extend ActiveSupport::Concern

    included do
    end

    module ClassMethods
      def acts_as_yaffle(options = {})
        cattr_accessor :yaffle_text_field
        self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
      end
    end
  end
end

ActiveRecord::Base.send :include, Yaffle::ActsAsYaffle
</ruby>

When you run +rake+ you should see the tests all pass:

<shell>
	5 tests, 5 assertions, 0 failures, 0 errors, 0 skips
</shell>

h4. Add an Instance Method

This plugin will add a method named 'squawk' to any Active Record objects that call 'acts_as_yaffle'. The 'squawk'
method will simply set the value of one of the fields in the database.

To start out, write a failing test that shows the behavior you'd like:

<ruby>
# yaffle/test/acts_as_yaffle_test.rb
require 'test_helper'

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_wickwalls_yaffle_text_field_should_be_last_tweet
    assert_equal "last_tweet", Wickwall.yaffle_text_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_wickwalls_squawk_should_populate_last_tweeted_at
    wickwall = Wickwall.new
    wickwall.squawk("Hello World")
    assert_equal "squawk! Hello World", wickwall.last_tweet
  end
end
</ruby>

Run the test to make sure the last two tests fail the an error that contains "NoMethodError: undefined method `squawk'",
then update 'acts_as_yaffle.rb' to look like this:

<ruby>
# yaffle/lib/yaffle/acts_as_yaffle.rb	

module Yaffle
  module ActsAsYaffle
    extend ActiveSupport::Concern

    included do
    end

    module ClassMethods
      def acts_as_yaffle(options = {})
        cattr_accessor :yaffle_text_field
        self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
      end
    end

    def squawk(string)
      write_attribute(self.class.yaffle_text_field, string.to_squawk)
    end

  end
end

ActiveRecord::Base.send :include, Yaffle::ActsAsYaffle
</ruby>

Run +rake+ one final time and you should see:
<shell>
	7 tests, 7 assertions, 0 failures, 0 errors, 0 skips
</shell>

NOTE: The use of +write_attribute+ to write to the field in model is just one example of how a plugin can interact with the model, and will not always be the right method to use. For example, you could also use <tt>send("#{self.class.yaffle_text_field}=", string.to_squawk)</tt>.

h3. Generators

Generators can be included in your gem simply by creating them in a lib/generators directory of your plugin. More information about
the creation of generators can be found in the "Generators Guide":generators.html

h3. Publishing your Gem

Gem plugins in progress can be easily be shared from any Git repository. To share the Yaffle gem with others, simply
commit the code to a Git repository (like Github) and add a line to the Gemfile of the any application:

<ruby>
gem 'yaffle', :git => 'git://github.com/yaffle_watcher/yaffle.git'	
</ruby>

After running +bundle install+, your gem functionality will be available to the application.

When the gem is ready to be shared as a formal release, it can be published to "RubyGems":http://www.rubygems.org.
For more information about publishing gems to RubyGems, see: "http://blog.thepete.net/2010/11/creating-and-publishing-your-first-ruby.html":http://blog.thepete.net/2010/11/creating-and-publishing-your-first-ruby.html

h3. Non-Gem Plugins

Non-gem plugins are useful for functionality that won't be shared with another project. Keeping your custom functionality in the
vendor/plugins directory un-clutters the rest of the application.

Move the directory that you created for the gem based plugin into the vendor/plugins directory of a generated Rails application, create a vendor/plugins/yaffle/init.rb file that contains "require 'yaffle'" and everything will still work.

<ruby>
# yaffle/init.rb

require 'yaffle'
</ruby>

You can test this by changing to the Rails application that you added the plugin to and starting a rails console. Once in the
console we can check to see if the String has an instance method of to_squawk.
<shell>
$ cd my_app
$ rails console
$ String.instance_methods.sort
</shell>

You can also remove the .gemspec, Gemfile and Gemfile.lock files as they will no longer be needed.

h3. RDoc Documentation

Once your plugin is stable 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. It's also customary to add '#:nodoc:' comments to those parts of the code that are not part of the public api.

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

<shell>
$ rake rdoc
</shell>

h4. References

* "Developing a RubyGem using Bundler":https://github.com/radar/guides/blob/master/gem-development.md
* "Using Gemspecs As Intended":http://yehudakatz.com/2010/04/02/using-gemspecs-as-intended/
* "Gemspec Reference":http://docs.rubygems.org/read/chapter/20
* "GemPlugins":http://www.mbleigh.com/2008/06/11/gemplugins-a-brief-introduction-to-the-future-of-rails-plugins
* "Keeping init.rb thin":http://daddy.platte.name/2007/05/rails-plugins-keep-initrb-thin.html

h3. Changelog

* March 10, 2011: Minor formatting tweaks.
* February 13, 2011: Get guide in synch with Rails 3.0.3. Remove information not compatible with Rails 3. Send reader elsewhere
for information that is covered elsewhere.
* April 4, 2010: Fixed document to validate XHTML 1.0 Strict. "Jaime Iniesta":http://jaimeiniesta.com
* November 17, 2008: Major revision by Jeff Dean