Engine Generator

2005-12-21

This article is obsolete now that Rails 2.3 has Engines in core.

Jon Lim on the Rails mailing list just announced the release of Engines Generator.

From the documentation:

$ script/generate engine UploadEngine
Please enter the author’s name: Joe Smith
Please enter the author’s email: joe.smith@xyz.com

We can generate the following licenses automatically for you:
0) None
1) GPL
2) MIT
3) LGPL
Please select a license: 2
‘MIT’ selected
exists vendor/plugins
create vendor/plugins/upload_engine
create vendor/plugins/upload_engine/README
create vendor/plugins/upload_engine/init_engine.rb
create vendor/plugins/upload_engine/app
create vendor/plugins/upload_engine/app/models
create vendor/plugins/upload_engine/app/controllers
create vendor/plugins/upload_engine/app/helpers
create vendor/plugins/upload_engine/app/views
create vendor/plugins/upload_engine/db
create vendor/plugins/upload_engine/db/migrate
create vendor/plugins/upload_engine/lib
create vendor/plugins/upload_engine/lib/upload_engine.rb
create vendor/plugins/upload_engine/lib/upload_engine
create vendor/plugins/upload_engine/public
create vendor/plugins/upload_engine/public/javascripts
create vendor/plugins/upload_engine/public/javascripts/upload_engine.js
create vendor/plugins/upload_engine/public/stylesheets
create vendor/plugins/upload_engine/public/stylesheets/upload_engine.css
create vendor/plugins/upload_engine/tasks
create vendor/plugins/upload_engine/tasks/upload_engine.rake
create vendor/plugins/upload_engine/test
create vendor/plugins/upload_engine/test/test_helper.rb
create vendor/plugins/upload_engine/test/fixtures
create vendor/plugins/upload_engine/test/functional
create vendor/plugins/upload_engine/test/unit

$ mv app/models/upload.rb vendor/plugins/upload_engine/app/models
$ mv app/controllers/upload_controller.rb vendor/plugins/upload_engine/app/controllers
$ mv app/views/upload vendor/plugins/upload_engine/app/views
$ mv public/javascripts/upload_engine.js vendor/plugins/upload_engine/public/javascripts
$ mv public/stylesheets/upload_engine.css vendor/plugins/upload_engine/public/stylesheets

config/environment.rb

1 Engines.start :upload_engine

$ script/server

This is way cool. Great work, Jon !

This article is obsolete since the bug was corrected in core a long time ago.

Seems there’s a problem with the Rails generator. I was receiving an odd (pun intended) error:


1 $ ruby script\generate migration -tc AddGamesAndCategories1
2 odd number of arguments for Hash
3 ./script/../config/../vendor/rails/railties/lib/rails_generator/scripts/../options.rb:130:in `[]’
4 ./script/../config/../vendor/rails/railties/lib/rails_generator/scripts/../options.rb:130:in `add_general_options!’
5 ./script/../config/../vendor/rails/railties/lib/rails_generator/scripts/../options.rb:130:in `call’
6 C:/ruby/lib/ruby/1.8/optparse.rb:1308:in `order!’
7 C:/ruby/lib/ruby/1.8/optparse.rb:1266:in `catch’
8 C:/ruby/lib/ruby/1.8/optparse.rb:1266:in `order!’
9 C:/ruby/lib/ruby/1.8/optparse.rb:1346:in `permute!’
10 C:/ruby/lib/ruby/1.8/optparse.rb:1373:in `parse!’
11 ./script/../config/../vendor/rails/railties/lib/rails_generator/scripts/../options.rb:89:in `parse!’
12 ./script/../config/../vendor/rails/railties/lib/rails_generator/scripts/../options.rb:85:in `initialize’
13 ./script/../config/../vendor/rails/railties/lib/rails_generator/scripts/../options.rb:85:in `new’
14 ./script/../config/../vendor/rails/railties/lib/rails_generator/scripts/../options.rb:85:in `parse!’
15 ./script/../config/../vendor/rails/railties/lib/rails_generator/scripts/../scripts.rb:19:in `run’
16 ./script/../config/../vendor/rails/railties/lib/commands/generate.rb:6
17 C:/ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:21:in `require__’
18 C:/ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:21:in `require’
19 script/generate:3

After a bit of debugging, it turned out that there’s a small problem with the Rails::Generator::Options::ClassMethods#add_general_options! method.



1 opt.on(-c, —svn,
2 Modify files with subversion. (Note: svn must be in path)) {
3 options[:svn] =
4 Hash`svn status`.collect { |e|
5 e.chop.split.reverse unless
6 e.chop.split.size != 2


1 opt.on(-c, —svn,
2 Modify files with subversion. (Note: svn must be in path)) {
3 options[:svn] =
4 Hash[
`svn status`.collect { |e|
5 e.chop.split.reverse unless
6 e.chop.split.size != 2 }.flatten] }

(reformatted for visibility)

This line will return nil, unless the line splits in two (A app/models/test.rb). The problem is that if the number of lines that don’t split in two is odd, then the flattened array will contain an odd number of items, which will cause Hash.new to fail.

The solution ? compact the array before flattening. I already submitted ticket #2814 with a patch.

In the meantime, I’m running a patched copy of Rails.

UPDATE: revision 2972 applied a modified version of my original patch.

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I am François Beausoleil, a Ruby on Rails and Scala developer. During the day, I work on Seevibes, a platform to measure social interactions related to TV shows. At night, I am interested many things. Read my biography.

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