TIL Rails: Extract methods to concerns easily

Author: stevenyap

rails/extract-methods-to-concerns-easily.md

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+# Extract methods to concerns easily
+
+A very easy way to extracts methods away from controllers and models is to use concerns.
+
+```ruby
+module TopicTracker
+  extend ActiveSupport::Concern
+  
+  def completed_topics_tracker
+    session[:completed_topics] ||= []
+  end
+end
+
+class OpinionsController < ApplicationController
+  include TopicTracker
+
+  def create
+    # method in concerns is available now
+    completed_topics_tracker << params.require(:topic_id)
+  end
+end
+```