Wrapping Rails controller logic within if statements

Question

I am trying to wrap my controller logic within the same conditional. Not sure how to achieve this as I am a bit new to ruby on rails. The pseudo code below is what I am trying to achieve

class Api::BaseController
  include Api::AuthConcern if SAME_CONDITION
  before_action -> { some_function() } if SAME_CONDITION

  if SAME_CONDITION
    rescue_from Api::AuthConcern::Unauthenticated do |e|
      render status: 401, json: { error: e.error }
    end

    rescue_from Api::AuthConcern::PermissionDenied do |e|
      render status: 403, json: { error: e.error }
    end
  end
end

Can you explain what problem this code is supposed to solve? It makes no sense at all as rescue_from is a class method used to handle exceptions. You have the if: and unless: options for callbacks (not the same thing as the ruby keyword) that take a lambda or a method name. — max
– max, Commented Sep 15, 2021 at 9:14
@max sorry for the confusion. What I am trying to do is actually wrap rescue, include, and before_action within a feature flag. If o activate the feature flag, then I’d like to enable the code wrapped in the conditional. — Liondancer
– Liondancer, Commented Sep 15, 2021 at 9:18
Is this flag class level? If so why not just place the code into a module (concern)? — max
– max, Commented Sep 15, 2021 at 9:21
The class body in Ruby is just a block of code thats evaluated in the context of the instance of Class so you can use whatever control structures you want. But I belive you're really going to regret adding a bunch of complexity as its going to be hard to test and lead to expected behavior as classes are persisted across requests by web servers that do forking. — max
– max, Commented Sep 15, 2021 at 9:24
A better idea is most like to just have your concern raise an exception and rescue it with a method which classes that include the module can override. — max
– max, Commented Sep 15, 2021 at 9:27

max · Accepted Answer · 2021-09-15 10:27:03Z

1

You ain't gonna need it. Just use methods instead:

module Api
  # Avoid adding "Concern" to your module names
  # it provides absolutely no information about what the object does
  module AuthConcern
    extend ActiveSupport::Concern

    included do
      rescue_from Unauthenticated { |e| respond_to_unauthenticated(e.error) }
      rescue_from PermissionDenied { |e| respond_to_permission_denied(e.error) } 
    end

    def respond_to_unauthenticated(message)
       render status: 401, json: { error: message }
    end

    def respond_to_permission_denied(message)
       render status: 403, json: { error: message }
    end
  end
end

This lets any class that includes the module customize the behavior by simply overriding the method:

module Api
  class FooController < BaseController
    # ...
  

    private  

    def respond_to_unauthenticated(error)
      render plain: 'Oh noes, you broke it!'
    end
  end
end

If you need to add more logic to to how a module augments the class with you can use the macro pattern. This is simply a class method that adds methods or behavior to the class:

module Api
  module AuthConcern
    extend ActiveSupport::Concern

    # ....

    module ClassMethods
      def authenticate!(**kwargs)
        before_action :authenticate!, **kwargs
      end
    end
  end
end

module Api
  class FooController < BaseController
    authenticate! except: :index
  end
end

This pattern is found all over Ruby in everything from attr_accessor to Rails callbacks and assocations.

edited Sep 15, 2021 at 10:27

answered Sep 15, 2021 at 9:47

max

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1 Comment

max Over a year ago

On a side note - do not use class Api::BaseController. Using the scope resolution operator does not set the correct module nesting and leads to suprising constant lookup and autoloading bugs. github.com/rubocop/ruby-style-guide#namespace-definition

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