[ruby-on-rails] Rails - How to use a Helper Inside a Controller

While I realize you are supposed to use a helper inside a view, I need a helper in my controller as I'm building a JSON object to return.

It goes a little like this:

def xxxxx

   @comments = Array.new

   @c_comments.each do |comment|
   @comments << {
     :id => comment.id,
     :content => html_format(comment.content)
   }
   end

   render :json => @comments
end

How can I access my html_format helper?

You can use

• helpers.<helper> in Rails 5+ (or ActionController::Base.helpers.<helper>)
• view_context.<helper> (Rails 4 & 3) (WARNING: this instantiates a new view instance per call)
• @template.<helper> (Rails 2)
• include helper in a singleton class and then singleton.helper
• include the helper in the controller (WARNING: will make all helper methods into controller actions)

In Rails 5+ you can simply use the function as demonstrated below with simple example:

module ApplicationHelper
  # format datetime in the format #2018-12-01 12:12 PM
  def datetime_format(datetime = nil)
    if datetime
      datetime.strftime('%Y-%m-%d %H:%M %p')
    else
      'NA'
    end
  end
end

class ExamplesController < ApplicationController
  def index
    current_datetime = helpers.datetime_format DateTime.now
    raise current_datetime.inspect
  end
end

OUTPUT

"2018-12-10 01:01 AM"

One alternative missing from other answers is that you can go the other way around: define your method in your Controller, and then use helper_method to make it also available on views as, you know, a helper method.

For instance:

class ApplicationController < ActionController::Base

private

  def something_count
    # All other controllers that inherit from ApplicationController will be able to call `something_count`
  end
  # All views will be able to call `something_count` as well
  helper_method :something_count 

end

class MyController < ApplicationController
    # include your helper
    include MyHelper
    # or Rails helper
    include ActionView::Helpers::NumberHelper

    def my_action
      price = number_to_currency(10000)
    end
end

In Rails 5+ simply use helpers (helpers.number_to_currency(10000))

In Rails 5 use the helpers.helper_function in your controller.

Example:

def update
  # ...
  redirect_to root_url, notice: "Updated #{helpers.pluralize(count, 'record')}"
end

Source: From a comment by @Markus on a different answer. I felt his answer deserved it's own answer since it's the cleanest and easier solution.

Reference: https://github.com/rails/rails/pull/24866

In rails 6, simply add this to your controller:

class UsersController < ApplicationController
  include UsersHelper
  
  # Your actions

end

Now the user_helpers.rb will be available in the controller.

In general, if the helper is to be used in (just) controllers, I prefer to declare it as an instance method of class ApplicationController.

My problem resolved with Option 1. Probably the simplest way is to include your helper module in your controller:

class ApplicationController < ActionController::Base
  include ApplicationHelper

...