= AttributeFu


Creating multi-model forms is amazingly easy with AttributeFu.

= Get It!

  $ piston import http://svn.jamesgolick.com/attribute_fu/tags/stable vendor/plugins/attribute_fu

= Conventions

attribute_fu requires the fewest keystrokes if you follow certain conventions.

* The partial that contains your associated model's form is expected to be called _class_name.template_ext
  (e.g. the partial for your Task model would be called _task.html.erb)
* The DOM element that contains the form for your model should have the CSS class .class_name
  (e.g. the CSS class for your Task would be .task)
* The DOM element that contains all of the rendered forms should have the DOM ID #class_name
  (e.g. the DOM ID of the container of your Task forms would be #tasks)
  <i>Note: This is only relevant if using the add_associated_link method.</i>

= Example

In this example, you'll build a form for a Project model, in which a list of associated (has_many) tasks can be edited. 

The first thing you need to do is enable attributes on the association.
  
  class Project < ActiveRecord::Base
    has_many :tasks, :attributes => true
  end

Instances of Project will now respond to task_attributes, whose format is as follows:
  
  @project.task_attributes = {
    @project.tasks.first.id => {:title => "A new title for an existing task"},
    :new => {
      "0" => {:title => "A new task"}
    }
  }
  
Any tasks that already exist in that collection, and are not included in the hash, as supplied to task_attributes, will be removed from the association when saved. Most of the time, the form helpers should take care of building that hash for you, though.

== Form Helpers

If you follow certain conventions, rendering your associated model's form elements is incredibly simple. The partial should have the name of the associated element's type, and look like a regular old form partial (no messy fields_for calls, or any nonsense like that).
  
  ## _task.html.erb
  <div class="task">
    <label>Title</label>
    <%= f.text_field :title %>
  </div>

Then, in your parent element's form, call the render_associated_form method on the form builder, with the collection of elements you'd like to render as the only argument.

  ## _form.html.erb
  <%= f.render_associated_form(@project.tasks) %>
  
That call will render the partial named _task.html.erb with each element in the supplied collection of tasks, wrapping the partial in a form builder (fields_for) with all the necessary arguments to produce a hash that will satisfy the task_attributes method.

You may want to add a few blank tasks to the bottom of your form; no need to do that in the controller anymore.

  <%= f.render_associated_form(@project.tasks, :new => 3) %>
  
Since this is Web2.0, no form would be complete without some DHTML add and remove buttons. Fortunately, there are some nifty helpers to create them for us. Simply calling remove_link on the form builder in your _task partial will do the trick.

  ## _task.html.erb
  <div class="task">
    <label>Title</label>
    <%= f.text_field :title %>
    <%= f.remove_link "remove" %>
  </div>
  
Creating the add button is equally simple. The add_associated_link helper will do all of the heavy lifting for you.

  ## _form.html.erb
  <%= f.add_associated_link "Add New Task", @project.tasks.build %>
  
That's all you have to do to create a multi-model form with attribute_fu!

== Discarding Blank Child Models

If you want to show a bunch of blank child model forms at the bottom of your form, but you only want to save the ones that are filled out, you can use the discard_if option. It accepts either a proc:

  class Project < ActiveRecord::Base
    has_many :tasks, :attributes => true, :discard_if => proc { |task| task.title.blank? }
  end

...or a symbol...

  class Project < ActiveRecord::Base
    has_many :tasks, :attributes => true, :discard_if => :blank?
  end
  
  class Task < ActiveRecord::Base
    def blank?
      title.blank?
    end
  end

Using a symbol allows you to keep code DRYer if you are using that routine in more than one place. Both of those examples, however, would have the same effect.

= Updates

Come join the discussion on the {mailing list}[link:http://groups.google.com/group/attribute_fu]

Updates will be available {here}[http://jamesgolick.com/attribute_fu]


== Credits

attribute_fu was created, and is maintained by {James Golick}[http://jamesgolick.com].



Copyright (c) 2007 James Golick, GiraffeSoft Inc., released under the MIT license