Question

Suppose I have a simple to-do list application. The application contains two models:

• lists (have an owner and description)
• items (have name and due-date) that belong to a specific list

I would like to have a single edit screen for a list in which I update the list attributes (such as description) and also create/delete/modify associated items. There should be a single “save” button that will commit all changes. Unless save is pressed, any change to the list and the items should be forgotten.

I wasn’t able to find an elegant best practice for this. Would greatly appreciate any suggestions and/or references to existing implementations.

Answer 1

You should be able to make this work with accepts_nested_attributes_for on the has_many association. Quoting from the Rails API docs:

Consider a member that has a number of
posts:

  class Member < ActiveRecord::Base
    has_many :posts
    accepts_nested_attributes_for :posts
  end

You can now set or update attributes
on an associated post model through
the attribute hash. For each hash that
does not have an id key a new record
will be instantiated, unless the hash
also contains a _delete key that
evaluates to true.

  params = { :member => {
    :name => 'joe', :posts_attributes => [
      { :title => 'Kari, the awesome Ruby documentation browser!' },
      { :title => 'The egalitarian assumption of the modern citizen' },
      { :title => '', :_delete => '1' } # this will be ignored
    ]
  }}

  member = Member.create(params['member'])
  member.posts.length # => 2
  member.posts.first.title # => 'Kari, the awesome Ruby documentation browser!'
  member.posts.second.title # => 'The egalitarian assumption of the modern citizen'

There’s also a good explanation in Railscast 196 which shows how to set up forms with nested attributes.