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.
rails g nested_form:install
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>
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.
First of all, thanks ro Ryan Bates for this gem. Awesome work.
This gem was originally based on the solution by Tim Riley in his complex-form-examples fork.
Andrea also wrote a great blog post on the internal workings of this gem.