Using the Rails ApplicationHelper in Grape

Question

I have a method defined in application_helper.rb:

def bayarea_cities
[
  ['San Francisco', 'San Francisco'],
  ['Berkeley', 'Berkeley'],
  ...
]
end

I'm also using Grape to create an API. It's in its own module outside the Rails app:

module FFREST
  class API_V2 < Grape::API
  ...

I'm pretty sure Grape is a Rack app, so it doesn't have normal access to the Rails modules. When I try to call the 'bayarea_cities' method in one of the API methods, I get an undefined variable or method error. I've tried include the ApplicationHelper module with 'include ApplicationHelper', but this did not work.

How can I get access to this inside the API class?

UPDATE:

Thanks for the update Deefour. I added extend self to my Helpers module, and referenced the methods as instance/mixin methods (not as module methods), but I'm still getting the same error. In my lib/helpers.rb file I have:

module Helpers
  extend self

  def bayarea_cities
    [
      'San Francisco',
      'Berkeley', 
      'Danville', 
      'Oakland',
      'Daly City', 
      'Sunnyvale'
    ]
  end 

  def us_states
    ['CA']
  end
end

and in my API file I have:

module FFREST
  class API_V1 < Grape::API
    include Helpers
    version 'v1', :using => :header, :vendor => 'feedingforward'
    ...

And of course, I have the config/initializers/helpers.rb file that says require "helpers"

But when I call the US states API method, for instance, by going to http://localhost:5000/api/states, I get:

undefined local variable or method `us_states' for #<Grape::Endpoint:0x007fd9d1ccf008>

Any ideas?

Answer 1

1. Create some lib/helpers.rb file with the contents: module Helpers; end
2. Move the bayarea_cities method into this module definition
3. Add a config/initializers/helpers.rb file containing require "helpers"
4. Inside the ApplicationHelpers class, add include Helpers
5. Inside your API_V2 class add include Helpers

You'll now have told Rails to make the Helpers module available within your application, and made bayarea_cities available as a method within both your Grape API class and your Rails app. The above are steps simply to get the point across - you need to put this common functionality in a place it can be easily accessed by any part of your application. You can (and should) use namespace your Helpers module.

---

Another tip: add extend self to the module to avoid the need to define everything as class methods as you mentioned in the comment

module Helpers
  extend self

  def bayarea_cities
    #...
  end
end

Finally, if you're including the module properly with include Helpers, you should be able to acces the method simply as bayarea_cities, not Helpers.bayarea_cities. If this isn't the case, you should definitely show the error you get so we can sort that out for you.