Defining Common Variables in Rails 5 Controllers

A memo on how to define common variables in Rails 5 controllers.

There are several ways to define common variables across controllers or the entire app in Rails applications. Here’s a summary of these methods and related information.

1. Defining in ApplicationController:

   class ApplicationController < ActionController::Base
     HASH_DATA = { value: "key" }
   end

   This method defines a constant available to all controllers and actions. The constant HASH_DATA is shared across the entire application.

2. Using before_action within a controller:

   class SomeController < ApplicationController
     before_action :set_admin
   
     def set_admin
       @listOfWords = ['a', 'b', 'c']
     end
   end

   This method uses before_action to define a common variable (in this case @listOfWords) within a specific controller. This variable is accessible from all actions in the controller.

3. Defining a method in ApplicationController:

   class ApplicationController < ActionController::Base
     def common_variable
       @listOfWords = ['a', 'b', 'c']
     end
   end

   This method adds a method to ApplicationController, and you can set common variables by calling this method in controllers. This is a flexible way to define variables, and you can call the common_variable method in controllers as needed.

The choice among these methods can be made flexibly according to your application’s requirements. Variables need to be defined as instance variables (@variable). Such variables are accessible in views, making them convenient for passing data from controllers to views.