Rails form_for_hash

Ruby on Rails has some nice form building helpers if you are building an HTML form for populating an ActiveRecord model. But what if you want your front end forms to not exactly map to your back end models? Maybe you are presenting a logical view that corresponds to parts of different models. Well, Rails still provides helpers that let you roll your own form. However, now you have to manually handle reading and writing values to the form. It would be nice if you could get the form_for functionality with just a simple Hash.

Well, it turns out that with a little bit of work, you can. Based on an idea I found at http://pullmonkey.com/2008/1/6/convert-a-ruby-hash-into-a-class-object/, I created a simple Object which wraps a Hash and behaves like an ActiveRecord. This class looks like:

class HashObject
  def initialize(hash={})
    @hash = hash
  end

  def method_missing(sym, *args, &block)
    @hash[sym]
  end
end

Then to make it easy to use, I put a helper function in helper/application_helper.rb

def form_for_hash(hash, name, url, html_options={}, &proc)
  object = HashObject.new(hash)
  form_for object, :as=>name, :url=>url, :html=>html_options, &proc
end

Now I can use it in the view as such:  (e.g. new.html.haml)

= form_for_hash @person, :person, special_people_path do

  = f.label :first_name, 'First Name'
  = f.text_field :first_name

  = f.label :last_name, 'Last Name'
  = f.text_field :last_name
  %br
  = f.label :phone_number, 'Phone Number'
  = f.text_field :phone_number
  -# etc etc etc

Then in your SpecialPeopleController you would have methods like

def new
  @person = {:first_name=>'Jenny', :phone_number=>'867-5309'}
end

def create
  @person = params[:person]
  # logic for populating/updating models based on hash goes here
end

And that is all you need to do to be able to use a Hash to populate your forms.