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Nested Form

This is a Rails gem for conveniently manage multiple nested models in a single form. It does so in an unobtrusive way through jQuery or Prototype.

This gem only works with Rails 3. See the rails2 branch for a plugin to work in Rails 2.

An example project showing how this works is available in the complex-nested-forms/nested_form branch.


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

gem "nested_form"

Next run the generator to create the JavaScript file. This will automatically detect if you are using jQuery or Prototype.

rails g nested_form:install

Running the generator will add a file at public/javascripts/nested_form.js which should be included after the jQuery or Prototype framework.

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


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 don't have the accepts_nested_attributes_for :tasks you'll get a Missing Block Error.

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>

SimpleForm and Formtastic Support

Use simple_nested_form_for or semantic_nested_form_for for SimpleForm and Formtastic support respectively. This is feature is not yet in a Gem release but is in the Git repo.


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.


If you are using jQuery, nested:fieldAdded and nested:fieldRemoved events are triggered on the form element after adding and removing fields.

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.

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