6. 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

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