title: Customizing or Overriding ActiveAdmin Edit/Update action controller
body: <p>I want to edit  'gca_user' model through ActiveAdmin  after some modification, when am click on 'Update' button it Should send a email to that user.</p>
  
  <p>using versions:
  ruby "2.1.5"
  Rails 4.2.1</p>
  
  <p>How can i do this?</p>
  
  <p>This is code:
  app/admin/gca_user.rb</p>
  
  <pre><code>ActiveAdmin.register GcaUser do
      permit_params :user_name, :first_name, :middle_name, :last_name, :cell_number, :social_media_provider, :social_media_id, :created_by, :created_date, :updataed_by, :updated_date, :realm, :username, :password, :credentials, :challenges, :email, :emailverified, :verificationtoken, :status, :created, :lastupdated, :provider, :nick_name
  
      index do
          selectable_column
          id_column
          column :user_name
          column :first_name
          column :middle_name
          column :last_name
          column :cell_number
          column :social_media_provider
          column :social_media_id
          column :created_by
          column :created_date
          column :updated_by
          column :updated_date
          column :realm
          column :username
          column :password
          column :credentials
          column :challenges
          column :email
          column :emailverified
          column :verificationtoken
          column :status
          column :created
          column :lastupdated
          column :provider
          column :nick_name
          actions
      end
  
      filter :id
      filter :user_name
      filter :first_name
      filter :middle_name
      filter :last_name
      filter :password
      filter :email
      filter :cell_number
      filter :social_media_provider
      filter :social_media_id
      filter :created_at
      form do |f|
          f.inputs "New User" do
              f.input :user_name
              f.input :first_name
              f.input :middle_name
              f.input :last_name
              f.input :cell_number
              f.input :social_media_provider
              f.input :social_media_id
              f.input :created_by
              f.input :created_date
              f.input :updated_by
              f.input :updated_date
              f.input :realm
              f.input :username
              f.input :password
              f.input :credentials
              f.input :challenges
              f.input :email
              f.input :emailverified
              f.input :verificationtoken
              f.input :status
              f.input :created
              f.input :lastupdated
              f.input :provider
              f.input :nick_name
          end
          f.actions
      end
  end
  </code></pre>
  
  <p>now following is my controller:</p>
  
  <p>app/controller/gca_user_controller.rb</p>
  
  <pre><code>class GcaUsersController &lt; InheritedResources::Base
      private
      def gca_user_params
          params.require(:gca_user).permit(:user_name, :first_name, :middle_name, :last_name, :cell_number, :social_media_provider, :social_media_id, :created_by, :created_date, :updataed_by, :updated_date, :realm, :username, :password, :credentials, :challenges, :email, :emailverified, :verificationtoken, :status, :created, :lastupdated, :provider, :nick_name )
      end
  end
  </code></pre>
  
  <p>following is my db-migrate file</p>
  
  <p>-db/migrate</p>
  
  <pre><code>class CreateGcaUsers &lt; ActiveRecord::Migration
      def change
          create_table :gca_users do |t|
              t.column :user_name, :string
              t.column :first_name, :string
              t.column :middle_name, :string
              t.column :last_name, :string
              t.column :cell_number, :string
              t.column :social_media_provider, :string
              t.column :social_media_id, :string
              t.column :created_by, :bigint
              t.column :created_date, :datetime
              t.column :updated_by, :bigint
              t.column :updated_date, :datetime
              t.column :realm, :string
              t.column :username, :string
              t.column :password, :string
              t.column :credentials, :string
              t.column :challenges, :string
              t.column :email, :string
              t.column :emailverified , :boolean
              t.column :verificationtoken, :string
              t.column :status, :string
              t.column :created, :datetime
              t.column :lastupdated, :datetime
              t.column :provider, :string
              t.column :nick_name, :string
          end
      end
  end
  </code></pre>
  
  <p>now please tell what should i do to full fill above requirement?</p>