Introducing AttributeFu: Multi-Model Forms Made Easy

Dec 01, 2007

Ever needed to create a form that works with two models? If you have, you know that it's a major pain. It really seems like it should be easier, doesn't it? Powerful, SQL-free associations join our models; helpers build our forms in fewer keystrokes than it takes to call somebody a fanboy in a digg comment. But, as soon as you want to put the pieces together — as soon as you seek multi-model form bliss, the whole system falls apart.

Ryan Bates has popularized a few recipes for cooking up just such a dish (we all owe that man a debt of gratitude, don't we?). Great solutions (thanks Ryan!). There are only two flaws to speak of.

  • AJAX-friendliness: What is this - web1? Maybe we should all build our sites in frames, and pepper them with blinking text.
  • It's not a plugin: You mean I have to write code!? I thought rails was going to wash my dishes, walk my dog, and build my websites, while I sat outside on the porch smoking cigars, praying to DHH.

Being the compulsive pluginizer that I am, I simply couldn't resist this great opportunity.


attribute_fu makes multi-model forms so easy you'll be telling all of your friends about it. Unless your friends are serious geeks, though, most of them will probably hang up on you. So, I recommend resisting that urge, unless you're looking for a good bedtime story.

To get started, enable attributes on your association (only has_many for now).

class Project < ActiveRecord::Base
  has_many :tasks, :attributes => true

Your model will then respond to task_attributes, which accepts a hash; the format of the which is a little bit different from what Ryan describes in his tutorials. Here's an example.

@project.task_attributes => { => {:title => "Wash the dishes"},
                     => {:title => "Go grocery shopping"},
                              :new => {
                                "0" => {:title => "Write a blog post about AttributeFu"}

Follow the rules, though, and attribute_fu will shield you from the ugly details.

Form Helpers

The plugin comes with a set of conventions (IM IN UR PROJECT, NAMIN UR PARTIALZ). Follow them, and building associated forms is as easy as it should be. Take note of the partial's name, and the conspicuously absent fields_for call.

## _task.html.erb
<p class="task">
  <label for="task_title">Title:</label><br/>
  <%= f.text_field :title %>

Rendering one or more of the above forms is just one call away.

## _form.html.erb
<div id="tasks">
  <%= f.render_associated_form(@project.tasks) %>

You may want to add a few blank tasks to the bottom of your form — formerly requiring an extra line in your controller.

<%= f.render_associated_form(@project.tasks, :new => 3) %>

This being web2.0, removing elements from the form with Javascript (but your boss calls it AJAX) is a must.

## _task.html.erb
<p class="task">
  <%= f.text_field :title %>
  <%= f.remove_link "remove" %>

Adding elements to the form via Javascript doesn't require any heavy lifting either.

## _form.html.erb
<%= f.add_associated_link('Add Task', %>

It's that easy.

Last but not least (okay, maybe least), if you're one of those people who just has to be different - who absolutely refuses to follow the rules, you can still use attribute_fu (I guess...). See the RDoc for how.

Plugins, Plugins, Get Your Plugins

$ piston import vendor/plugins/attribute_fu

Check out the RDoc for more details.

Come join the discussion on the mailing list.