Question

I am using Ruby on Rails 3 and I would like to move some custom and shared code in a module.

1. What syntax should I use to write the module code?
2. In which folder of my application I have to place the module file?
3. How I have to include that module in one or more controller classes?
4. What other action, if any, do I have to use the custom module anywhere in my application?
5. How can I call methods in the module from my application?

Answer 1

To 1. A module is created/opened
by simply saying:

module MyModule
  def first_module_method
  end
end

To 2. The lib folder. If you want to organize your modules in the lib folder, you can put them into modules themselves. For example, if you wanted a subfolder super_modules your modules would be defined as follows:

module SuperModules
  module MyModule
    def first_module_method
    end
  end
end

To 3./5. When including the module in a class you can simply call the modules methods as if they were defined within the class:

class MyClass
  include MyModule
  def some_method
    first_module_method #calls module method
  end
end

To 4.
Frst, make sure that your module is really needed in every class of your application. If it isn’t it makes sense to only include it where it is need so as not to bloat the classes that don’t need it anyways. If you really want the module everywhere, include look at the class hierarchy of your classes in the app. Do you want the module in all models? You could open ActiveRecord::Base and add add your module there.