How to handle nested resources/routes correctly?

Question

I am trying to build a Rails app modded from Michael Hartl's Railstutorial. The code is located on GitHub.

I am using the following nested resources:

resources :users do
  resources :scaffolds
end

But I am getting the following error:

ActionView::Template::Error (undefined method `scaffolds_path' for #<#    <Class:0x007f87848019d0>:0x007f8782651948>):
4: 
5: <div class="row">
6:   <div class="span6 offset3">
7:     <%= form_for(@scaffold) do |f| %>
8:       <%= render 'shared/error_messages', object: f.object %>
9:       <%= f.text_field :name,        placeholder: "Scaffold name" %>
10:       <%= f.text_area  :description, placeholder: "Description" %> 
app/views/scaffolds/new.html.erb:7:in `_app_views_scaffolds_new_html_erb___1119296061714080468_70109999031900'

I am puzzled why it is looking for scaffolds_path and not user_scaffolds_path?

The @scaffold is created in the app/controller/scaffolds_controller.rb:

def new
  @scaffold = current_user.scaffolds.build
end

Inspecting the @scaffold object thus created shows:

'#<Scaffold id: nil, name: nil, description: nil, tax_id: nil, user_id: 36, created_at: nil, updated_at: nil>'

Dumping the methods of @scaffold don't reveal any scaffolds_path or user_scaffolds_path methods which suggest additional problems?

The users model has_many :scaffolds and the scaffold model belongs_to :user.

Answer 1

The reason for the missing methods is that form_for in the view are not aware we are nesting. This is fixed by feeding it an array:

form_for([@user, @scaffold])

Answer 2

It has to do with the form helper. IF you're using nested resources and you never want to perform controller actions on Scaffold objects directly, then you need to do the following in your form view and model. Something like:

# app/models/user.rb
class User < ActiveRecord::Base
  ...

  accepts_nested_attributes_for :scaffolds
end

...and in the view...

<%= form_for(@user) do |f| %>
  ...
  <%= fields_for @user.scaffold do |scaffold_fields| %>

...this will result in the path for the fields_for giving you the expected users_scaffolds_path

NOTE that the specifics of how you use the fields_for helper changes depending on whether it's a has_one or has_many relationship and such. The first time through this you may just tear your hair out - so fair warning.

If, on the other hand...

...you want to use Scaffold objects on their own and as part of a nested route, you can declare the route twice - once for when you want to use it as a nested resource, and once when you want to use it on its own.

# config/routes.rb
resources :users do
  resources :scaffolds
end

resources :scaffolds

With this, when you run rake routes you'll see both users_scaffolds_path and scaffolds_path for all the standard actions.