Nested Form

Conveniently manage multiple nested models in a single form. It does so in an unobtrusive way through jQuery.

This gem works with Rails 3+.

Setup

Add it to your Gemfile then run bundle to install it.

gem 'nested_form'

And then add it to the Asset Pipeline in app/assets/javascripts/application.js file:

//= require jquery_nested_form

Non Asset Pipeline Setup

If you do not use the asset pipeline, run this generator to create the JavaScript file.

rails g nested_form:install

You can then include the generated JavaScript in your layout.

<%= javascript_include_tag :defaults, "nested_form" %>

Rails 5+ and Webpacker

As Nested Form is a very old project, support for a NPM package was never provided and although being old enough, this gem works fine with newer versions of Rails up until 5.2.3.

If you're using webpacker and want to introduce Nested Form to your project, you can use the NPM verion that is just an entrypoint to the file located in vendor/assets/javascripts/jquery_nested_form.

You can manually download the file and import it as well but I wanted to try publishing it to NPM.

Add it to your project with:

$ yarn add jquery_nested_form

And import it in your application.js pack:

import 'jquery_nested_form'

Usage

• Strong Parameters
• SimpleForm and Formtastic Support
• Partials
• Specifying target when adding Nested Fields
• Specifying wrapper to remove Nested Fields

Imagine you have a Project model that has_many :tasks. To be able to use this gem, you'll need to add accepts_nested_attributes_for :tasks to your Project model. If you wish to allow the nested objects to be destroyed, then add the :allow_destroy => true option to that declaration.

See the accepts_nested_attributes_for documentation for details on all available options.

This will create a tasks_attributes= method, so you may need to add it to the attr_accessible array (attr_accessible :tasks_attributes).

Then use the nested_form_for helper method to enable the nesting.

<%= nested_form_for @project do |f| %>

You will then be able to use link_to_add and link_to_remove helper methods on the form builder in combination with fields_for to dynamically add/remove nested records.

<%= f.fields_for :tasks do |task_form| %>
  <%= task_form.text_field :name %>
  <%= task_form.link_to_remove "Remove this task" %>
<% end %>
<p><%= f.link_to_add "Add a task", :tasks %></p>

In order to choose how to handle, after validation errors, fields that are marked for destruction, the marked_for_destruction class is added on the div if the object is marked for destruction.

Strong Parameters

For Rails 4+ here is an example:

params.require(:project).permit(:name, tasks_attributes: [:id, :name, :_destroy])

The :id is to make sure you do not end up with a whole lot of tasks.

The :_destroy must be there so that we can delete tasks.

SimpleForm and Formtastic Support

Use simple_nested_form_for or semantic_nested_form_for for SimpleForm and Formtastic support respectively.

Partials

It is often desirable to move the nested fields into a partial to keep things organized. If you don't supply a block to fields_for it will look for a partial and use that.

<%= f.fields_for :tasks %>

In this case it will look for a partial called "task_fields" and pass the form builder as an f variable to it.

Specifying target when adding Nested Fields

By default, link_to_add appends fields immediately before the link when clicked. This is not desirable when using a list or table, for example. In these situations, the "data-target" attribute can be used to specify where new fields should be inserted.

<table id="tasks">
  <%= f.fields_for :tasks, :wrapper => false do |task_form| %>
    <tr class="fields">
      <td><%= task_form.text_field :name %></td>
      <td><%= task_form.link_to_remove "Remove this task" %></td>
    </tr>
  <% end %>
</table>
<p><%= f.link_to_add "Add a task", :tasks, :data => { :target => "#tasks" } %></p>

Specifying wrapper to remove Nested Fields

By default, link_to_remove works by hiding all fields wrapped in div element with .fields class.

Having this wrapper is completely optional and can be disabled with wrapper: false. However, when disabling the wrapper, link_to_remove stops working because it needs to somehow reference the DOM element that holds all fields to "remove".

When using wrapper: false, normally one would introduce a default wrapper. Maybe because of a normal wrapper like a bootstrap .row.

In those cases, the custom wrapper class name should be specify in the link_to_remove helper:

<%= f.link_to_remove 'Quitar', data: { wrapper: '.row' } %>

Notice the use of CSS dot notation for class name .row

JavaScript events

Sometimes you want to do some additional work after element was added or removed, but only after DOM was really modified. In this case simply listening for click events on 'Add new'/'Remove' link won't reliably work, because your code and code that inserts/removes nested field will run concurrently.

This problem can be solved, because after adding or removing the field a set of custom events is triggered on this field. Using form example from above, if you click on the "Add a task" link, nested:fieldAdded and nested:fieldAdded:tasks will be triggered, while nested:fieldRemoved and nested:fieldRemoved:tasks will be triggered if you click "Remove this task" then.

These events bubble up the DOM tree, going through form element, until they reach the document. This allows you to listen for the event and trigger some action accordingly. Field element, upon which action was made, is passed along with the event object. In jQuery you can access it via event.field.

For example, you have a date input in a nested field and you want to use jQuery datepicker for it. This is a bit tricky, because you have to activate datepicker after field was inserted.

See example below for jQuery:

$(document).on('nested:fieldAdded', function(event){
  // this field was just inserted into your form
  var field = event.field; 
  // it's a jQuery object already! Now you can find date input
  var dateField = field.find('.date');
  // and activate datepicker on it
  dateField.datepicker();
})

Second type of event (i.e. nested:fieldAdded:tasks) is useful then you have more than one type of nested fields on a form (i.e. tasks and milestones) and want to distinguish, which exactly was added/deleted.

See also how to limit max count of nested fields

Enhanced jQuery JavaScript template

You can override default behavior of inserting new subforms into your form. For example:

window.nestedFormEvents.insertFields = function(content, assoc, link) {
  return $(link).closest('form').find(assoc + '_fields').append($(content));
}

Contributing

If you have any issues with Nested Form not addressed above or in the example project, please add an issue on GitHub or fork the project and send a pull request. To run the specs:

bundle install
bundle exec rake spec:install
bundle exec rake db:migrate
bundle exec rake spec:all

See available rake tasks using bundle exec rake -T.

Special Thanks

This gem was originally based on the solution by Tim Riley in his complex-form-examples fork.

Thank you Andrew Manshin for the Rails 3 transition, Andrea Singh for converting to a gem and Peter Giacomo Lombardo for Prototype support.

Andrea also wrote a great blog post on the internal workings of this gem.

Thanks Pavel Forkert for the SimpleForm and Formtastic support.