Setup a nested form with Cocoon

cocoon.rb

# Add to gemfile
gem 'cocoon'

# In application.js
//= require cocoon

# For a ticket, with associated ticket_comments

class Ticket < ActiveRecord::Base
  has_many :ticket_comments,  inverse_of: :ticket_detail
  accepts_nested_attributes_for :ticket_comments, allow_destroy: true
  validates_associated  :ticket_comments
end

class TicketComment < ActiveRecord::Base

  belongs_to :ticket_detail, inverse_of: :ticket_comments, touch: true, required: true				
  
  paginates_per 50

  validates_length_of :name, maximum: 255
  validates_presence_of :description
  validates_uniqueness_of :message_id, :allow_nil => true, :allow_blank => true
  
  default_scope {order(:created_at)}
end

# In the controller permit the related parameters.  You should also look up the comments, either using .includes(:ticket_comments) or a separate query.
class TicketsController < ApplicationController
  
  private
  def ticket_params
    params.require(:ticket).permit(:location_id, :user_id, :name, ticket_comments_attributes: [:ticket_detail_id, :description, :public, :created_by_id, :updated_by_id, :_destroy, attachments: []]).                                    merge(updated_by_id: current_user.id)
  end
  
end

# If you use a decorator file
class TicketDecorator < Draper::Decorator
	delegate_all
	decorates_association :ticket_comments
end


# In the view, show the list of comments, then allow the user to add a comment using the cocoon gem:

<div>                  
  <%= render :partial => 'ticket_comments/ticket_comment', collection: @ticket_comments, cache: Proc.new{ |ticket_comment| [current_user.locale, current_user.has_permission?(:yapster_push), ticket_comment, 'tc_panel_line']} %>

  <%= f.fields_for :ticket_comments do |tc| %>
    <% if tc.object.try(:new_record?) && !tc.object.description.blank? %>
      <br />
      <%= render partial: 'ticket_comment_fields', locals: {f: tc} %>
    <% end %>
  <% end %>
  <div>
    <div class="actions">
      <%= f.submit 'Update', wrapper: { class: 'btn btn-primary'} %> <!--Duplicate Submit button for whole form-->
      <%= link_to_add_association 'Add Update', f, :ticket_comments, :class => "btn btn-primary" %>
    </div>
  </div>
</div>

# Create a new parial called _ticket_comment_fields.html.erb.  You will pass the form f to this parital
<div class = "nested-fields">
  <fieldset>
    <div class="media-body">
      <p><strong><%= current_user.display_name %></strong> said:</p>
      <small class="text-muted"><%= Time.current %></small>
      
      <div>
        <%= f.check_box :public, label: 'Publish' if current_user.has_permission? :publish %>
        <%= f.text_area :description, hide_label: true  %>
      </div>

      <div class="actions">
        <%= link_to_remove_association '  Remove', f,  :class => "btn btn-xs btn-danger fa fa-trash-o" %>
      </div>
    </div>
  </fieldset>
</div>