ActiveModel - View - Controller in Rails instead of ActiveRecord?

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:

<

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.

Answer 2

Looks like you should have instead investigated the (not very well documented) ActiveModel::Conversions class

https://github.com/rails/rails/blob/3-1-stable/activemodel/lib/active_model/conversion.rb

  include ActiveModel::Conversion

  def persisted?
    false
  end

would have done the trick, same applies to Rails 4.2