Copy a controller class instance variables - ruby-on-rails

Question

I want to write a simple erb template generator to parse stored erb templates from the views using Generator module. I call the Generator from the rails controller to generate it's singleton instances and pass it the WallController by self pointer.
require 'generator'
class WallController < ApplicationController
def index
header = File.read 'app/views/application-header.html'.freeze
#instances = {header: header}
# Load view generators
Generator.generate_instances self
end
end
The first thing Generator.generate_instances actually attempts to do is to copy the WallController instance variables (hence the self pointer) to perform correct parsing of the erb templates. Then it generates methods returning erb resulted text.
require 'erb'
module Generator
def self.generate_instances environment
# Mimic class environment
if environment.superclass == ApplicationController
environment.instance_variables.each do |v|
puts "Copy instance variable '#{v}' from #{environment.name} to #{self.name}"
value = environment.instance_variable_get(v)
self.send :instance_variable_set, v, value
end
end
# Parse the ERB templates
templates = #instances
return 0 if !templates.is_a?(Hash) or templates.empty?
templates.keys.each.with_index do |key, index|
define_singleton_method key do
ERB.new(templates.values[index]).result
end
end
end
end
Usage of Generator interface will look like this:
<%=== Generator.header %>
I am new to rails but I have found out that rails controller's included files are limited to a single static structure. I didn't manage either to overwrite class Object or class Class singleton methods which could be helpful.
However, after running the above example the instance variables of WallController return the WallController class address in stead of values defined by WallController.index.
undefined method `empty?' for #<WallController:0x000000000a1f90>
Is there a correct way to distribute a rails controller instance variables among other controllers? If not, why are regular instance copy not working?
If I had to write it in ruby, that would be easy:
module Y
def self.generate_environment environment
environment.instance_variables.each do |v|
puts "Copy #{v} from #{environment.name} to #{self.name}"
value = environment.instance_variable_get v
self.instance_variable_set(v, value)
end if environment.class == Class
puts "Retrived string: #{#hello}"
end
end
class X
def self.index
#hello = 'Hello, World!'
Y.generate_environment self
end
end
X.index

Answer 1

This problem may be solved with viewcomponent, which allows for standard ruby code for the view controller. Also solves the problem of dividing the view code to smaller reusable components in reasonable speed.
To use the viewcomponent gem first include it to your Gemfile.
gem 'view_component', require: 'view_component/engine'
After updating your gems with bundle install, you will also need to restart your server if it's running, to apply the new gem.
Then generating the component is similar in usage to other rails generators. The first argument is a component name and the second is a component argument.
rails generate component Header site_id
Now I focus on files generated in app/component directory, view and controller code. This will simply be the controller to create the header snippet of the view.
Inside of app/component/header_component.rb can be encapsulated all the code from WallController related to the header view.
class HeaderComponent < ViewComponent::Base
def initialize(site_id:)
puts "Rendering header component for site: #{site_id}"
# Load site elements
#site = Site.find site_id
#menu_items = []
Site.all.each.with_index do |site, index|
#menu_items.push site.title => site.link
end
end
end
Similarly, put all the header view erb code to the app/component/header.html.erb.
The finished component can be generated from the view using rails render:
<%= render HeaderComponent.new(site_id: 1) %>