cocoon/README.markdown

# cocoon

[![Build Status](https://travis-ci.org/nathanvda/cocoon.png)](https://travis-ci.org/nathanvda/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.

This project is not related to [Apache Cocoon](http://cocoon.apache.org/)

## 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:

````ruby
gem "cocoon"
````

### Rails 3.1+

Add the following to `application.js` so it compiles to the
asset_pipeline

````ruby
//= require cocoon
````

### Rails 3.0.x

If you are using Rails 3.0.x, you need to run the installation task (since rails 3.1 this is no longer needed):

````ruby
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:

````haml
= javascript_include_tag :cocoon
````

or using erb, you write

````ruby
<%= javascript_include_tag :cocoon %>
````

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

## Usage

Suppose you have a model `Project`:

````ruby
rails g scaffold Project name:string description:string
````

and a project has many `tasks`:

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

Edit the models to code the relation:

````ruby
class Project < ActiveRecord::Base
  has_many :tasks
  accepts_nested_attributes_for :tasks, :reject_if => :all_blank, :allow_destroy => true
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:

````haml
= 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.actions do
    = f.action :submit
````

and inside the `_task_fields` partial we write:

````haml
.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 [cocoon_formtastic_demo](https://github.com/nathanvda/cocoon_formtastic_demo).

### Using simple_form

Inside our `projects/_form` partial we then write:

````haml
= simple_form_for @project do |f|
  = f.input :name
  = f.input :description
  %h3 Tasks
  #tasks
    = f.simple_fields_for :tasks do |task|
      = render 'task_fields', :f => task
    .links
      = link_to_add_association 'add task', f, :tasks
  = f.submit
````

and inside the `_task_fields` partial we write:

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

There is an example project on github implementing it called [cocoon_simple_form_demo](https://github.com/nathanvda/cocoon_simple_form_demo).

### Using standard rails forms

Inside our `projects/_form` partial we then write:

````haml
- form_for @project do |f|
  .field
    = f.label :name
    %br
    = f.text_field :name
  .field
    = f.label :description
    %br
    = f.text_field :description
  %h3 Tasks
  #tasks
    = f.fields_for :tasks do |task|
      = render 'task_fields', :f => task
    .links
      = link_to_add_association 'add task', f, :tasks
  = f.submit
````

and inside the `_task_fields` partial we write:

````haml
.nested-fields
  .field
    = f.label :description
    %br
    = f.text_field :description
  .field
    = f.check_box :done
    = f.label :done
  = link_to_remove_association "remove task", f
````

I will provide 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 some special options, the first three allow to control the placement of the new link-data:
  - `data-association-insertion-traversal` : the jquery traversal method to allow node selection relative to the link. `closest`, `next`, `children`, etc. Default: absolute selection
  - `data-association-insertion-node` : the jquery selector of the node
  - `data-association-insertion-method` : jquery method that inserts the new data. `before`, `after`, `append`, `prepend`, etc. Default: `before`
  - `data-association-insertion-position` : old method specifying where to insert new data.
      - this setting still works but `data-association-insertion-method` takes precedence. may be removed in a future version.
  - `partial`: explicitly declare the name of the partial that will be used
  - `render_options` : options passed through to the form-builder function (e.g. `simple_fields_for`, `semantic_fields_for` or `fields_for`).
                       If it contains a `:locals` option containing a hash, that is handed to the partial.
  - `wrap_object` : a proc that will allow to wrap your object, especially useful if you are using decorators (e.g. draper). See example lower.
  - `force_non_association_create`: if true, it will _not_ create the new object using the association (see lower)

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).

#### :render_options
Inside the `html_options` you can add an option `:render_options`, and the containing hash will be handed down to the form-builder for the inserted
form. E.g. especially when using `twitter-bootstrap` and `simple_form` together, the `simple_fields_for` needs the option `:wrapper => 'inline'` which can
be handed down as follows:

(Note: In certain newer versions of simple_form, the option to use is ':wrapper => 'bootstrap')

````haml
= link_to_add_association 'add something', f, :something, :render_options => {:wrapper => 'inline' }
````

If you want to specify locals that needed to handed down to the partial, write

````haml
= link_to_add_association 'add something', f, :something, :render_options => {:locals => {:sherlock => 'Holmes' }}
````


#### :partial

To overrule the default partial name, e.g. because it shared between multiple views, write

````haml
= link_to_add_association 'add something', f, :something, :partial => 'shared/something_fields'
````

#### :wrap_object

If you are using decorators, the normal instantiation of the associated will not be enough, actually you want to generate the decorated object.

A simple decorator would look like:

```
class CommentDecorator
  def initialize(comment)
    @comment = comment
  end

  def formatted_created_at
    @comment.created_at.to_formatted_s(:short)
  end

  def method_missing(method_sym, *args)
    if @comment.respond_to?(method_sym)
      @comment.send(method_sym, *args)
    else
      super
    end
  end
end
```

To use this, write

```
link_to_add_association('add something', @form_obj, :comments, :wrap_object => Proc.new {|comment| CommentDecorator.new(comment) })
```

Note that the `:wrap_object` expects an object that is _callable_, so any `Proc` will do. So you could as well use it to do some fancy extra initialisation (if needed).
But note you will have to return the (nested) object you want used.
E.g.


```
link_to_add_association('add something', @form_obj, :comments, 
                        :wrap_object => Proc.new { |comment| comment.name = current_user.name; comment })
```

#### :force_non_association_create

In normal cases we create a new nested object using the association relation itself. This is the cleanest way to create
a new nested object. But this has a side-effect: for each call of `link_to_add_association` a new element is added to the association.

In most cases this is not a problem, but if you want to render a `link_to_add_association` for each nested element this will result
in an infinite loop.

To resolve this, specify that `:force_non_association_create` should be `true`, as follows:

```
link_to_add_association('add something', @form_obj, :comments, :force_non_association_create => true)
```

By default `:force_non_association_create` is `false`.

> A cleaner option would be to call a function that performs this initialisation and returns `self` at the end.

### 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).


### Callbacks (upon insert and remove of items)

On insertion or removal the following events are triggered:

* `cocoon:before-insert`: called before inserting a new nested child
* `cocoon:after-insert`: called after inserting
* `cocoon:before-remove`: called before removing the nested child
* `cocoon:after-remove`: called after removal

To listen to the events, you to have the following code in your javascript:

    $('#container').bind('cocoon:before-insert', function(e, inserted_item) {
        // ... do something
    });

where `e` is the event and the second parameter is the inserted or removed item. This allows you to change markup, or
add effects/animations (see example below).


If in your view you have the following snippet to select an `owner`
(we use slim for demonstration purposes)

````haml
#owner
  #owner_from_list
    = f.association :owner, :collection => Person.all(:order => 'name'), :prompt => 'Choose an existing owner'
  = link_to_add_association 'add a new person as owner', f, :owner
````

This view part will either let you select an owner from the list of persons, or show the fields to add a new person as owner.


The callbacks can be added as follows:

````javascript
$(document).ready(function() {
    $('#owner').bind('cocoon:before-insert',
         function() {
           $("#owner_from_list").hide();
           $("#owner a.add_fields").hide();
         });
    $('#owner').bind('cocoon:after-insert',
         function() {
           /* ... do something ... */
         });
    $('#owner').bind("cocoon:before-remove",
         function() {
           $("#owner_from_list").show();
           $("#owner a.add_fields").show();
         });
    $('#owner').bind("cocoon:after-remove",
         function() {
           /* e.g. recalculate order of child items */
         });

    // example showing manipulating the inserted/removed item

    $('#tasks').bind('cocoon:before-insert', function(e,task_to_be_added) {
        task_to_be_added.fadeIn('slow');
    });

    $('#tasks').bind('cocoon:after-insert', function(e, added_task) {
        // e.g. set the background of inserted task
        added_task.css("background","red");
    });

    $('#tasks').bind('cocoon:before-remove', function(e, task) {
        // allow some time for the animation to complete
        $(this).data('remove-timeout', 1000);
        task.fadeOut('slow');
    })


});
````

Do note that for the callbacks to work there has to be a surrounding container (div), where you can bind the callbacks to.


When adding animations and effects to make the removal of items more interesting, you will also have to provide a timeout.
This is accomplished by the following line:

    $(this).data('remove-timeout', 1000);

Note that you could also immediately add this to your view (on the `.nested-fields` container).

### Control the Insertion behaviour

The default insertion location is at the back of the current container. But we have added two `data`-attributes that are read to determine the insertion-node and -method.

For example:

````javascript
$(document).ready(function() {
    $("#owner a.add_fields").
      data("association-insertion-method", 'before').
      data("association-insertion-node", 'this');
});
````

The `association-insertion-node` will determine where to add it. You can choose any selector here, or specify this (default it is the parent-container).

The `association-insertion-method` will determine where to add it in relation with the node. Any jQuery DOM Manipulation method can be set but we recommend sticking to any of the following: `before`, `after`, `append`, `prepend`. It is unknown at this time what others would do.

The `association-insertion-traversal` will allow node selection to be relative to the link.

For example:

````javascript
$(document).ready(function() {
    $("#owner a.add_fields").
      data("association-insertion-method", 'append').
      data("association-insertion-traversal", 'closest').
      data("association-insertion-node", '#parent_table');
});
````

### Partial

If no explicit partial-name is given, `cocoon` looks for a file named `_<association-object_singular>_fields`.
To override the default partial-name use the option `:partial`.

For the javascript to behave correctly, the partial should start with a container (e.g. `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.


## Contributors

The list of contributors just keeps on growing. [Check it out](https://github.com/nathanvda/cocoon/graphs/contributors) !!
I would really really like to thank all of them,
they make cocoon more awesome every day. Thanks.

## 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.

## Not Related To Apache Cocoon

Please note that this project is not related to the Apache Cocoon web framework project. 

[Apache Cocoon](http://cocoon.apache.org/), Cocoon, and Apache are either registered trademarks or trademarks of the [Apache Software Foundation](http://www.apache.org/) in the United States and/or other countries.