cocoon

cocoon is a Rails3 gem to allow easier handling of nested forms.

Nested forms are forms that handle nested models and attributes in one form. For example a project with its tasks, an invoice with its ordered items.

It is formbuilder-agnostic, so it works with standard Rails, or Formtastic or simple_form.

Prerequisites

This gem uses jQuery, it is most useful to use this gem in a rails3 project where you are already using jQuery.

Furthermore i would advice you to use either formtastic or simple_form.

I have a sample project where I demonstrate the use of cocoon with formtastic.

Installation

Inside your Gemfile add the following:

gem "cocoon"

Run the installation task:

rails g cocoon:install

This will install the needed javascript file. Inside your application.html.haml you will need to add below the default javascripts:

= javascript_include_tag :cocoon

or using erb, you write

<%= javascript_include_tag :cocoon %>

That is all you need to do to start using it!

Usage

Suppose you have a model Project:

rails g scaffold Project name:string description:string

and a project has many tasks:

rails g model Task description:string done:boolean project_id:integer

Edit the models to code the relation:

class Project < ActiveRecord::Base
  has_many :tasks
  accepts_nested_attributes_for :tasks
end

class Task < ActiveRecord::Base
  belongs_to :project
end

What we want to achieve is to get a form where we can add and remove the tasks dynamically. What we need for this, is that the fields for a new/existing task are defined in a partial view called _task_fields.html.

We will show the sample usage with the different possible form-builders.

Using formtastic

Inside our projects/_form partial we then write:

- f.inputs do
  = f.input :name
  = f.input :description
  %h3 Tasks
  #tasks
    = f.semantic_fields_for :tasks do |task|
      = render 'task_fields', :f => task
    .links
      = link_to_add_association 'add task', f, :tasks
  -f.buttons do
    = f.submit 'Save'

and inside the _task_fields partial we write:

.nested-fields
  = f.inputs do
    = f.input :description
    = f.input :done, :as => :boolean
    = link_to_remove_association "remove task", f

That is all there is to it!

There is an example project on github implementing it called formtastic-cocoon-demo.

Using simple_form

This is almost identical to formtastic, instead of writing semantic_fields_for you write simple_fields_for.

There is an example project on github implementing it called cocoon_simple_form_demo.

Using standard rails forms

I will provide a full example (and a sample project) later.

How it works

I define two helper functions:

link_to_add_association

This function will add a link to your markup that will, when clicked, dynamically add a new partial form for the given association. This should be placed below the semantic_fields_for.

It takes four parameters:

• name: the text to show in the link
• f: referring to the containing form-object
• association: the name of the association (plural) of which a new instance needs to be added (symbol or string).
• html_options: extra html-options (see link_to) There are two extra options that allow to conrol the placement of the new link-data:
  • data-association-insertion-node : the jquery selector of the node
  • data-association-insertion-position : insert the new data before or after the given node.

Optionally you could also leave out the name and supply a block that is captured to give the name (if you want to do something more complicated).

There is an option to add a callback on insertion. The callback can be added as follows:

$("#todo_tasks a.add_fields").
  data("insertion-callback",
     function() {
       $(this).find("textarea").autoResize({extraSpace:0}).change();
     });

link_to_remove_association

This function will add a link to your markup that will, when clicked, dynamically remove the surrounding partial form. This should be placed inside the partial _<association-object-singular>_fields.

It takes three parameters:

• name: the text to show in the link
• f: referring to the containing form-object
• html_options: extra html-options (see link_to)

Optionally you could also leave out the name and supply a block that is captured to give the name (if you want to do something more complicated).

Partial

The partial should be named _<association-object_singular>_fields, and should start with a div of class .nested-fields.

There is no limit to the amount of nesting, though.

Note on Patches/Pull Requests

• Fork the project.
• Make your feature addition or bug fix.
• Add tests for it. This is important so I don't break it in a future version unintentionally.
• Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
• Send me a pull request. Bonus points for topic branches.

Todo

• add more sample relations: has_many :through, belongs_to, ...
• improve the tests (test the javascript too)(if anybody wants to lend a hand ...?)

Copyright

Copyright (c) 2010 Nathan Van der Auwera. See LICENSE for details.