Ruby on rails: singular resource and form_for

Question

I want user to work with only one order connected to user's session. So I set singular resource for order

routes.rb:

resource :order

views/orders/new.html.erb:

<%= form_for @order do |f| %>
   ...
<% end %>

But when I open the new order page I get an error:

undefined method `orders_path`

I know, that I can set :url => order_path in form_for, but what is the true way of resolving this collision?

Answer 1

Unfortunately, this is a bug. You'll have to set the url like you mention.

= form_for @order, :url => orders_path do |f|

Answer 2

Where does that magic path come from?

It took me a lot of tracing but I ultimately found that the url_for determines the path for your model using the polymorphic_path method defined in ActionDispatch::Routing::PolymorphicRoutes. polymorphic_path ultimately gets the automagic path for your model by calling something along the lines of:

record.class.model_name.route_key

I'm simplifying slightly but this is basically it. If you have an array (e.g. form_for[@order, @item]) the above is called on each element and the results are joined with _.

The model_name method on your Class comes from ActiveRecord::Naming.

module ActiveModel
  ...
  module Naming
    ...
    def model_name
      @_model_name ||= begin
        namespace = self.parents.detect do |n|
          n.respond_to?(:use_relative_model_naming?) && 
                                                 n.use_relative_model_naming?
        end
        ActiveModel::Name.new(self, namespace)
      end
    end
  end
end

How can I change it?

Fortunately ActiveModel::Name precalculates all values including route_key, so to override that value all we have to do is change the value of the instance variable.

For the :order resource in your question:

class Order < ActiveRecord::Base
  model_name.instance_variable_set(:@route_key, 'order')
  ...
end

# new.html.erb
<%= form_for @order do |f| # Works with action="/order" %>
    ...
<% end %>

Try it out!