Question

I’m trying to use ActiveModel instead of ActiveRecord for my models because I do not want my models to have anything to do with the database.

Below is my model:

class User
  include ActiveModel::Validations
  validates :name, :presence => true
  validates :email, :presence => true
  validates :password, :presence => true, :confirmation => true

  attr_accessor :name, :email, :password, :salt
  def initialize(attributes = {})
    @name  = attributes[:name]
    @email = attributes[:email]
    @password = attributes[:password]
    @password_confirmation = attributes[:password_confirmation]
  end
end

And here’s my controller:

class UsersController < ApplicationController
  def new
    @user = User.new
    @title = "Sign up"
  end
end

And my view is:

<h1>Sign up</h1>

<%= form_for(@user) do |f| %>
<div class="field">
    <%= f.label :name %><br />
    <%= f.text_field :name %>
</div>
<div class="field">
    <%= f.label :email %><br />
    <%= f.text_field :email %>
</div>
<div class="field">
    <%= f.label :password %><br />
    <%= f.password_field :password %>
</div>
<div class="field">
    <%= f.label :password_confirmation, "Confirmation" %><br />
    <%= f.password_field :password_confirmation %>
</div>
<div class="actions">
    <%= f.submit "Sign up" %>
</div>
<% end %>

But when I load this view in the browser, I am getting an exception:

undefined method 'to_key' for User:0x104ca1b60

Can anyone please help me with this?

Many thanks in advance!

Answer 1

I went rooting around the Rails 3.1 source to sort this out, I figured that would be easier than searching anywhere else. Earlier versions of Rails should be similar. Jump to the end if tl;dr.

---

When you call form_for(@user), you end going through this:

def form_for(record, options = {}, &proc)
  #...
  case record
  when String, Symbol
    object_name = record
    object      = nil
  else
    object      = record.is_a?(Array) ? record.last : record
    object_name = options[:as] || ActiveModel::Naming.param_key(object)
    apply_form_for_options!(record, options)
  end

And since @user is neither a String nor Object, you go through the else branch and into apply_form_for_options!. Inside apply_form_for_options! we see this:

as = options[:as]
#...
options[:html].reverse_merge!(
  :class  => as ? "#{as}_#{action}" : dom_class(object, action),
  :id     => as ? "#{as}_#{action}" : dom_id(object, action),
  :method => method
)

Pay attention to that chunk of code, it contains both the source of your problem and the solution. The dom_id method calls record_key_for_dom_id which looks like this:

def record_key_for_dom_id(record)
  record = record.to_model if record.respond_to?(:to_model)
  key = record.to_key
  key ? sanitize_dom_id(key.join('_')) : key
end

And there’s your call to to_key. The to_key method is defined by ActiveRecord::AttributeMethods::PrimaryKey and since you’re not using ActiveRecord, you don’t have a to_key method. If you have something in your model that behaves like a primary key then you could define your own to_key and leave it at that.

But, if we go back to apply_form_for_options! we’ll see another solution:

as = options[:as]

So you could supply the :as option to form_for to generate a DOM ID for your form by hand:

<%= form_for(@user, :as => 'user_form') do |f| %>

You’d have to make sure that the :as value was unique within the page though.

---

Executive Summary:

• If your model has an attribute that behaves like a primary key, then define your own to_key method that returns it.
• Or, supply an appropriate :as option to form_for.