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abyme is the modern way to handle dynamic nested forms in Rails 6+.
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abyme 🕳

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abyme is an easy and form-agnostic way to handle nested attributes in Rails, using stimulus under the hood. Here's an example :

# views/projects/_form.html.erb
<%= form_for @project do |f| %>
  <%= f.text_field :title %>
  <%= f.text_area :description %>
  <%= f.abyme_for(:tasks) %>
  <%= f.submit 'Save' %>
<% end %>

Supposing you have a Project that has_many :tasks and a partial located in views/abyme/_task_fields containing your form fields for tasks, the abyme_for command will generate and display 3 elements in this order :

  • A div containing all task fields for @project.tasks (either persisted or already built instances of tasks)
  • A div which will contain all additional tasks about to be created (added through the Add task button below)
  • A button to generate fields for new instances of tasks

Have a look below to learn more about configuration and all its different options.

Demo app

Demo preview

Check out our demo app here :

Source code is right here :


Add this line to your application's Gemfile:

gem 'abyme'

And then execute:

$ bundle
$ yarn add abyme

IMPORTANT : With the launch of Stimulus V3 (which introduced a lot of changes), the connection with the AbymeController won't work. Please, make sure you're using Stimulus V2 for now.

If you don't have Stimulus installed yet, please run :

yarn add stimulus@2.0.0

With Stimulus installed, you need to register the stimulus controller that takes care of the JavaScript behaviour. You can launch this generator :

rails generate abyme:stimulus

Or you can register it yourself :

// app/javascript/controllers/index.js
import { Application } from "stimulus"
import { definitionsFromContext } from "stimulus/webpack-helpers"
// Add this line below
import { AbymeController } from 'abyme'

const application = Application.start()
const context = require.context("controllers", true, /_controller\.js$/)
// And this one
application.register('abyme', AbymeController)

Getting started

To learn more about the why of this gem, check out our wiki

You may also check out our step by step tutorial and our advanced configuration guide (currently in construction).


As in our our tutorial, we'll assume we have a Project model, that has_many :tasks for the rest of the documentation.


To be up and running in no time, we built a few generators. Feel free to skip these if you prefer a manual implementation.


To generate everything you need with one command, use this generator :

rails generate abyme:resource project tasks
# Includes configuration in Project model
# Adds abyme_attributes in ProjectsController permitted params
# Creates a partial and minimum boilerplate in app/views/abyme/_task_fields.html.erb

Now, head to your parent form and keep reading !

You can also specify attributes to be permitted, or permit all of them (see below). This will populate the partial with input fields for the specified attributes

rails generate abyme:resource project tasks description title
# Includes configuration in Project model, including permitted attributes
# Adds abyme_attributes in ProjectsController permitted params
# Creates a partial with input fields for the specified attributes in app/views/abyme/_task_fields.html.erb

Individual generators

All the generators launched by the main resource generator are available individually :

# Controller
rails generate abyme:controller Projects

# Model
# Permit only a few attributes
rails generate abyme:model project tasks description title
# Permit all attributes
rails generate abyme:model project participants all_attributes

# Views
# Without attributes (use this if you're not using SimpleForm or don't care about generating input fields)
rails generate abyme:view tasks
# With a few attributes
rails generate abyme:view tasks name description
# With all attributes
rails generate abyme:view tasks all_attributes


💡 Don't forget to include Abyme::Model in your parent model

#abymize(:association, permit: nil, reject: nil, options = {})

In models, the abyme_for :association acts as an alias for this command :

  accepts_nested_attributes_for :association, reject_if: :all_blank, :allow_destroy: true
  • permit: [] : allows you to generate a hash of attributes that can be easily called on the controller side through the ::abyme_attributes class method (see details below).
  abymize :association, permit: [:name, :description]
  # You may also permit all attributes like so :
  abymize :association, permit: :all_attributes 
  • reject: [] : allows you to add all attributes to ::abyme_attributes, excepted the ones specified.
  abymize :association, reject: [:password]
  • options: {} : [the same options] you may pass to the accepts_nested_attributes method (see this link for details)
  abyme_for :association, limit: 3, allow_destroy: false


Returns a hash to the right format to be included in the strong params on the controller side. For a Project model with nested :tasks :

  # => {tasks_attributes: [:title, :description, :id, :_destroy]}



Infers the name of the resource from the controller name, and calls the ::abyme_attributes method on it. Hence, in your ProjectsController :

  def project_params
    params.require(:project).permit(:title, :description, abyme_attributes)


#abyme_for(:association, options = {}, &block)

This is the container for all your nested fields. It takes the symbolized association as a parameter, along with options, and an optional block to specify any layout you may wish for the different parts of the abyme builder.

💡 Please note an id is automatically added to this element, which value is : abyme--association_name.

💡 If you don't pass a block, records, new_records and add_association will be called and will appear in this order in your layout.

  • partial: : allows you to indicate a custom partial path for both records and new_records
  <%= f.abyme_for(:tasks, partial: 'projects/task_fields') do |abyme| %>
    <%= abyme.records %>
    <%= abyme.new_records %>
    <%= add_associated_record %>
  <% end %>
  • limit: : allows you to limit the number of new fields that can be created through JS. If you need to limit the number of associations in database, you will need to add validations. You can also pass an option in your model as well.
  <%= f.abyme_for(:tasks, limit: 5) do |abyme| %>
    # Beyond 5 tasks, the add button won't add any more fields. See events section below to see how to handle the 'abyme:limit-reached' event
    <%= abyme.records %>
    <%= abyme.new_records %>
    <%= add_associated_record %>
  <% end %>
  • min_count: : by default, there won't be any blank fields added on page load. By passing a min_count option, you can set how many empty fields should appear in the form.
  <%= f.abyme_for(:tasks, min_count: 1) do |abyme| %>
    # 1 blank task will automatically be added to the form.
    <%= abyme.records %>
    <%= abyme.new_records %>
    <%= add_associated_record %>
  <% end %>
  • locals: {} : allows you to pass some arbitrary variables to your partial.
<%= f.abyme_for(:comments, locals: {count: 0}) %>

The count variable will be available in _comment_fields.html.erb and equal 0 for both new and persisted records. If you need to differentiate between both, you can pass the same option to either #records and #new_records (see below)

If you're not passing a block, the abyme_for method can take a few additional options:

  • button_text: this will set the add_association button text to the string of your choice.

💡 All options that should be passed to either records or new_records below can be passed here and will be passed down.


A few options can be passed to abyme.records:

  • collection: : allows you to pass a collection of your choice to only display specific objects.
  <%= f.abyme_for(:tasks) do |abyme| %>
    <%= abyme.records(collection: @project.tasks.where(done: false)) %>
    <%= abyme.new_records %>
    <%= add_associated_record %>
  <% end %>
  • order: : allows you to pass an ActiveRecord order method to sort your instances the way you want.
  <%= f.abyme_for(:tasks) do |abyme| %>
    <%= abyme.records(order: { created_at: :asc }) %>
    <%= abyme.new_records %>
    <%= add_associated_record %>
  <% end %>
  • partial: : allows you to indicate a custom partial, if one has not already been passed to abyme_for.
  <%= f.abyme_for(:tasks) do |abyme| %>
    <%= abyme.records %>
    <%= abyme.new_records(partial: 'projects/task_fields') %>
    <%= add_associated_record %>
  <% end %>
  • fields_html: : gives you the possibility to add any HTML attribute you may want to each set of fields. By default, an abyme--fields and an singular_association-fields class are already present.
  <%= f.abyme_for(:tasks) do |abyme| %>
    <%= abyme.records(fields_html: { class: "some-class" }) %>
    # Every set of persisted fields will have these 3 classes : 'abyme--fields', 'task-fields', and 'some-class'
    <%= abyme.new_records %>
    <%= add_associated_record %>
  <% end %>
  • wrapper_html: : gives you the possibility to add any HTML attribute you may want to the wrapper containing all persisted fields.
  <%= f.abyme_for(:tasks) do |abyme| %>
    <%= abyme.records(wrapper_html: { class: "persisted-records" }) %>
    # The wrapper containing all persisted task fields will have an id "abyme-tasks-wrapper" and a class "persisted-records"
    <%= abyme.new_records %>
    <%= add_associated_record %>
  <% end %>
  • locals: {} : allows you to pass some arbitrary variables to your partial. When passed to either #records or #new_records, the value will be different depending on whether the record for which the partial is called is persisted or not
<%= f.abyme_for(:tasks) do |abyme| %>
  <%= abyme.records(locals: {count: 1}) %>
  <%= abyme.new_records(locals: {count: 2} %>
  <%= add_associated_record(content: 'Add task' %>
<% end %>

In _task_fields.html.erb, if the record has been dynamically added with the "Add" button, the countvariable will be equal to 2. If the record has been loaded from existing associations, it will equal 1.


Here are the options that can be passed to abyme.new_records:

  • position: : allows you to specify whether new fields added dynamically should go at the top or at the bottom. :end is the default value.
  <%= f.abyme_for(:tasks) do |abyme| %>
    <%= abyme.records %>
    <%= abyme.new_records(position: :start) %>
    <%= add_associated_record %>
  <% end %>
  • partial: : same as #records
  • fields_html: : same as #records
  • wrapper_html: : same as #records
    • locals: : same as #records

#add_associated_record, #remove_associated_record

These 2 methods behave the same. Here are their options :

  • tag: : allows you to specify a tag of your choosing, like :a, or :div. Default is :button.
  • content: : the text to display inside the element. Default is Add association_name
  • html: : gives you the possibility to add any HTML attribute you may want to the element.
  <%= f.abyme_for(:tasks) do |abyme| %>
    # ...
    <%= add_associated_record(tag: :a, content: "Add a super task", html: {id: "add-super-task"}) %>
  <% end %>

As you may have seen above, you can also pass a block to the method to give it whatever HTML content you want :

  <%= f.abyme_for(:tasks) do |abyme| %>
    # ...
    <%= add_associated_record(tag: :div, html: {id: "add-super-task", class: "flex"}) do %>
      <i class="fas fa-plus"></i>
      <h2>Add a super task</h2>
    <% end %>
  <% end %>


This part is still a work in progress and subject to change. We're providing some basic self-explanatory events to attach to. These are emitted by the main container (created by the abyme_for method).

We're currently thinking about a way to attach to these via Stimulus. Coming soon !

Lifecycle events

  • abyme:before-add
  • abyme:after-add
  • abyme:before-remove
  • abyme:after-remove
document.getElementById('abyme--tasks').addEventListener('abyme:before-add', yourCallback)

Other events

  • abyme:limit-reached
const tasksContainer = document.getElementById('abyme--tasks');
tasksContainer.addEventListener('abyme:limit-reached', () => { 
  alert('You reached the max number of tasks !')


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.


Bug reports and pull requests are welcome on GitHub at


The gem is available as open source under the terms of the MIT License.