Ruby on Rails Guides: Rails Application Templates

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## Rails Application Templates

Application templates are simple Ruby files containing DSL for adding plugins/gems/initializers etc. to your freshly created Rails project or an existing Rails project.

By referring to this guide, you will be able to:

- Use templates to generate/customize Rails applications
- Write your own reusable application templates using the Rails template API

### Chapters

1. Usage
2. Template API
   - gem(name, options = {})
   - gem_group(*names, &block)
   - add_source(source, options = {})
   - plugin(name, options = {})
   - vendor/lib/file/initializer(filename, data = nil, &block)
   - rakefile(filename, data = nil, &block)
   - generate(what, args)
   - run(command)
   - rake(command, options = {})
   - route(routing_code)
   - inside(dir)
   - ask(question)
   - yes?(question) or no?(question)
   - git(:command)

### 1 Usage

To apply a template, you need to provide the Rails generator with the location of the template you wish to apply, using -m option. This can either be path to a file or a URL.

    $ rails new blog -m ~/template.rb
    $ rails new blog -m http://example.com/template.rb

You can use the rake task `rails:template` to apply templates to an existing Rails application. The location of the template needs to be passed in to an environment variable named LOCATION. Again, this can either be path to a file or a URL.

    $ rake rails:template LOCATION=~/template.rb
    $ rake rails:template LOCATION=http://example.com/template.rb

### 2 Template API

Rails templates API is very self explanatory and easy to understand. Here’s an example of a typical Rails template:

    # template.rb
    run "rm public/index.html"
    generate(:scaffold, "person name:string")
    route "root :to => 'people#index'"
    rake("db:migrate")

    git :init
    git :add => "."
    git :commit => "-a -m 'Initial commit'"

The following sections outlines the primary methods provided by the API:

#### 2.1 gem(name, options = {})

Adds a `gem` entry for the supplied gem to the generated application’s `Gemfile`.

For example, if your application depends on the gems `bj` and `nokogiri`:

    gem "bj"
    gem "nokogiri"

Please note that this will NOT install the gems for you and you will have to run `bundle install` to do that.

    bundle install

#### 2.2 gem_group(*names, &block)

Wraps gem entries inside a group.

For example, if you want to load `rspec-rails` only in `development` and `test` group:

    gem_group :development, :test do
      gem "rspec-rails"
    end

#### 2.3 add_source(source, options = {})

Adds the given source to the generated application’s `Gemfile`.

For example, if you need to source a gem from “http://code.whytheluckystiff.net”:

    add_source "http://code.whytheluckystiff.net"

#### 2.4 plugin(name, options = {})

Installs a plugin to the generated application.

Plugin can be installed from Git:

    plugin 'authentication', :git => 'git://github.com/foor/bar.git'

You can even install plugins as git submodules:

    plugin 'authentication', :git => 'git://github.com/foor/bar.git',
                             :submodule => true

Please note that you need to `git :init` before you can install a plugin as a submodule.

Or use plain old SVN:

    plugin 'usingsvn', :svn => 'svn://example.com/usingsvn/trunk'

#### 2.5 vendor/lib/file/initializer(filename, data = nil, &block)

Adds an initializer to the generated application’s `config/initializers` directory.

Lets say you like using `Object#not_nil?` and `Object#not_blank?`:

    initializer 'bloatlol.rb', <<-CODE
    class Object
      def not_nil?
        !nil?
      end

      def not_blank?
        !blank?
      end
    end
    CODE

Similarly `lib()` creates a file in the `lib/` directory and `vendor()` creates a file in the `vendor/` directory.

There is even `file()`, which accepts a relative path from `Rails.root` and creates all the directories/file needed:

    file 'app/components/foo.rb', <<-CODE
    class Foo
    end
    CODE

That’ll create `app/components` directory and put `foo.rb` in there.

#### 2.6 rakefile(filename, data = nil, &block)

Creates a new rake file under `lib/tasks` with the supplied tasks:

    rakefile("bootstrap.rake") do
      <<-TASK
        namespace :boot do
          task :strap do
            puts "i like boots!"
          end
        end
      TASK
    end

The above creates `lib/tasks/bootstrap.rake` with a `boot:strap` rake task.

#### 2.7 generate(what, args)

Runs the supplied rails generator with given arguments.

    generate(:scaffold, "person", "name:string", "address:text", "age:number")

#### 2.8 run(command)

Executes an arbitrary command. Just like the backticks. Let’s say you want to remove the `public/index.html` file:

    run "rm public/index.html"

#### 2.9 rake(command, options = {})

Runs the supplied rake tasks in the Rails application. Let’s say you want to migrate the database:

    rake "db:migrate"

You can also run rake tasks with a different Rails environment:

    rake "db:migrate", :env => 'production'

#### 2.10 route(routing_code)

This adds a routing entry to the `config/routes.rb` file. In above steps, we generated a person scaffold and also removed `public/index.html`. Now to make `PeopleController#index` as the default page for the application:

    route "root :to => 'person#index'"

#### 2.11 inside(dir)

Enables you to run a command from the given directory. For example, if you have a copy of edge rails that you wish to symlink from your new apps, you can do this:

    inside('vendor') do
      run "ln -s ~/commit-rails/rails rails"
    end

#### 2.12 ask(question)

`ask()` gives you a chance to get some feedback from the user and use it in your templates. Lets say you want your user to name the new shiny library you’re adding:

    lib_name = ask("What do you want to call the shiny library ?")
    lib_name << ".rb" unless lib_name.index(".rb")

    lib lib_name, <<-CODE
    class Shiny
    end
    CODE

#### 2.13 yes?(question) or no?(question)

These methods let you ask questions from templates and decide the flow based on the user’s answer. Lets say you want to freeze rails only if the user want to:

    rake("rails:freeze:gems") if yes?("Freeze rails gems ?")
    no?(question) acts just the opposite.

#### 2.14 git(:command)

Rails templates let you run any git command:

    git :init
    git :add => "."
    git :commit => "-a -m 'Initial commit'"

### Feedback

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