The Rails framework provides a large number of helpers for working with assets, dates, forms, numbersand Active Record objects, to name a few. These helpers are available to all templates by default.

In addition to using the standard template helpers provided in the Rails framework, creating custom helpers to extract complicated logic or reusable functionality is strongly encouraged. By default, the controller will include a helper whose name matches that of the controller, e.g., MyControllerwill automatically include MyHelper.

Additional helpers can be specified using the helperclass method in ActionController::Baseor any controller which inherits from it.

Examples

The to_smethod from the Time class can be wrapped in a helper method to display a custom message if the Time object is blank:

module FormattedTimeHelper
  def format_time(time, format=:long, blank_message=" ")
    time.blank? ? blank_message : time.to_s(format)
  end
end

FormattedTimeHelper can now be included in a controller, using the helperclass method:

class EventsController < ActionController::Base
  helper FormattedTimeHelper
  def index
    @events = Event.find(:all)
  end
end

Then, in any view rendered by EventController, the format_timemethod can be called:

<% @events.each do |event| -%>
  <p>
    <% format_time(event.time, :short, "N/A") %> | <%= event.name %>
  </p>
<% end -%>

Finally, assuming we have two event instances, one which has a time and one which does not, the output might look like this:

23 Aug 11:30 | Carolina Railhawks Soccer Match
N/A | Carolina Railhaws Training Workshop
Methods
H
Instance Public methods
helper(*args, &block)

The helperclass method can take a series of helper module names, a block, or both.

  • *args: One or more modules, strings or symbols, or the special symbol :all.

  • &block: A block defining helper methods.

Examples

When the argument is a string or symbol, the method will provide the “_helper” suffix, require the file and include the module in the template class. The second form illustrates how to include custom helpers when working with namespaced controllers, or other cases where the file containing the helper definition is not in one of Rails' standard load paths:

helper :foo             # => requires 'foo_helper' and includes FooHelper
helper 'resources/foo'  # => requires 'resources/foo_helper' and includes Resources::FooHelper

When the argument is a module it will be included directly in the template class.

helper FooHelper # => includes FooHelper

When the argument is the symbol :all, the controller will include all helpers beneath ActionController::Base.helpers_dir (defaults to app/helpers /*.rbunder RAILS_ROOT).

helper :all

Additionally, the helperclass method can receive and evaluate a block, making the methods defined available to the template.

# One line
helper { def hello() "Hello, world!" end }
# Multi-line
helper do
  def foo(bar)
    "#{bar} is the very best"
  end
end

Finally, all the above styles can be mixed together, and the helpermethod can be invoked with a mix of symbols, strings, modulesand blocks.

helper(:three, BlindHelper) { def mice() 'mice' end }
# File actionpack/lib/action_controller/helpers.rb, line 114
def helper(*args, &block)
  args.flatten.each do |arg|
    case arg
      when Module
        add_template_helper(arg)
      when :all
        helper(all_application_helpers)
      when String, Symbol
        file_name  = arg.to_s.underscore + '_helper'
        class_name = file_name.camelize
        begin
          require_dependency(file_name)
        rescue LoadError => load_error
          requiree = / -- (.*?)(\.rb)?$/.match(load_error.message).to_a[1]
          if requiree == file_name
            msg = "Missing helper file helpers/#{file_name}.rb"
            raise LoadError.new(msg).copy_blame!(load_error)
          else
            raise
          end
        end
        add_template_helper(class_name.constantize)
      else
        raise ArgumentError, "helper expects String, Symbol, or Module argument (was: #{args.inspect})"
    end
  end
  # Evaluate block in template class if given.
  master_helper_module.module_eval(&block) if block_given?
end
helper_attr(*attrs)

Declares helper accessors for controller attributes. For example, the following adds new nameand name=instance methods to a controller and makes them available to the view:

helper_attr :name
attr_accessor :name
# File actionpack/lib/action_controller/helpers.rb, line 178
def helper_attr(*attrs)
  attrs.flatten.each { |attr| helper_method(attr, "#{attr}=") }
end
helper_method(*methods)

Declare a controller method as a helper. For example, the following makes the current_usercontroller method available to the view:

class ApplicationController < ActionController::Base
  helper_method :current_user, :logged_in?
  def current_user
    @current_user ||= User.find_by_id(session[:user])
  end
   def logged_in?
     current_user != nil
   end
end

In a view:

<% if logged_in? -%>Welcome, <%= current_user.name %><% end -%>
# File actionpack/lib/action_controller/helpers.rb, line 163
def helper_method(*methods)
  methods.flatten.each do |method|
    master_helper_module.module_eval <<-end_eval
      def #{method}(*args, &block)                    # def current_user(*args, &block)
        controller.send(%(#{method}), *args, &block)  #   controller.send(%(current_user), *args, &block)
      end                                             # end
    end_eval
  end
end
helpers()

Provides a proxy to access helpers methods from outside the view.

# File actionpack/lib/action_controller/helpers.rb, line 183
def helpers
  unless @helper_proxy
    @helper_proxy = ActionView::Base.new
    @helper_proxy.extend master_helper_module
  else
    @helper_proxy
  end
end