Cool Nested Forms

Gem Version
Add dynamically generated forms to your model’s form for any of its associations. For example if you have a Job model that has_many Task then this gem will assist you in adding all the JavaScript necessary to allow your users to click an “Add Task” button on your edit view, the view will then append a new form to the DOM with all the field attributes formatted for rails (id, name, etc) plus will add any necessary hidden fields for existing records (

There is also JS events raised when an entry is added or removed so you can hook up your code for pre-form submission editing.

Any entries added or removed won’t update the DB until the form is submitted.


Add this line to your application’s Gemfile:
$ gem 'cool_nested_forms'

And then execute:
$ bundle install

Or install it yourself as:
$ gem install cool_nested_forms

Then require the JavaScript in your app/assets/javascripts/application.js
//= require cool_nested_forms

Usage Example

For this example I will use Job and Task models

Preparing your models

Job Model

class Job < ApplicationRecord 
  has_many :tasks, :dependent => :destroy

  # we need to accepts_nested_attributes_for Task
  # :name is required in this example - Use your own required field here or remove the reject_if call
  # :allow_destroy => true so we can delete entries when passing the _destroy field
  accepts_nested_attributes_for :tasks, :reject_if => lambda { |a| a[:name].blank? }, :allow_destroy => true

Task Model

class Task < ApplicationRecord
  belongs_to :job

Preparing the Job Controller

class JobsController < ApplicationController
  # include the CoolNestedFormsHelper 
  helper CoolNestedFormsHelper

  # other code

  def job_params
    # :id and :_destroy are required. Substitute name with your own fields 
    params.require(:job).permit(:name, :tasks_attributes => [:id, :name, :_destroy])

The partials used to generate the new and existing tasks

We need to provide cool_nested_forms two partials. One for new and one
for existing records. They will be placed under the Job's view folder. Make sure the
id field of the container is set like so: id="<%= id %>"


<%= builder.hidden_field :_destroy, :class => 'cnf-removable' %> <%= builder.label :name %> <%= builder.text_field :name %> <%= remove_entry_button "Remove", Task, {:target => id} %>


<%= builder.hidden_field :_destroy, :class => 'cnf-removable' %> <%= builder.hidden_field :id %> <%= builder.label :name %> <%= builder.text_field :name %> <%= remove_entry_button "Remove", Task, {:target => id} %>

Adding functionality to the Job form


<%= form_with(model: job, local: true) do |form| %>


    <%= new_entry_template(form,Task) %>

    <%= new_entry_button("Add Task", Task )%>

   <%= entries_container(form,Task,job.tasks) %>

 <% end %>;

After add/remove events

If you need to perform any other javascript actions after an entry is added or
removed, you can add a listener to these events

Something like this

$(document).bind('coolNestedForms.childAdded', function(){
  // do something


Bug reports and pull requests are welcome on GitHub at This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [Contributor Covenant]( code of conduct.


The gem is available as open source under the terms of the [MIT License](