Singularize resource routes, if it is singular!

In most cases plural routes (read Simple RESTful Ruby on Rails routes) are needed to deal with the resources. But sometimes it makes sense to have only a singular resource routing.
Whenever a resource is singular (like Singletons) or singular in the current context, its routes should be singular as well. Reasons are:

1. Expressiveness (to express the resource is singular)
2. Less routes (singular resources have no index route for returning collections)
3. Resource ID can be hidden (the object can be found anyway)

For example the original plural routes to the users profile (routes.rb):

resources :profiles, except: [:index, :destroy]

for the model:

class Profile < ActiveRecord::Base
  belongs_to :user
  validates :user, presence: true
end

give access to the RESTful controller (profiles_controller.rb):

class ProfilesController < ApplicationController
  def show
    @profile = Profile.find params[:id]
  end

  def new
    @profile = Profile.new user_id: user.id
  end

  def create
    @profile = Profile.new user_id: user.id
    @profile.attributes = params[:profile]
    render(action: :new) unless @profile.save
  end

  def edit
    @profile = Profile.find params[:id]
  end

  def update
    @profile = Profile.find params[:id]
    @profile.attributes = params[:profile]
    render(action: :edit) unless @profile.save
  end
private
  def user
    @user = User.find session[:user_id]
  end
end

in the view:

  <%= link_to 'Profile', profiles_path(@user.profile) %>

A user can have only one profile. It can created, updated, but not deleted. After the user accounted, the User object is always present. That is why the Profile ID is not required to be parameterized.

Refactoring starts with singularizing the routes (routes.rb):

resource :profile, except: :destroy

to the refactored controller (profiles_controller.rb):

class ProfilesController < ApplicationController
  def show
    @profile = user.profile
  end

  def new
    @profile = user.build_profile
  end

  def create
    @profile = user.build_profile
    @profile.attributes = params[:profile]
    render(action: :new) unless @profile.save
  end

  def edit
    @profile = user.profile
  end

  def update
    @profile = user.profile
    @profile.attributes = params[:profile]
    render(action: :edit) unless @profile.save
  end
private
  def user
    @user = User.find session[:user_id]
  end
end

and the refactored link in the view:

  <%= link_to 'Profile', profile_path %>

Please note the ProfilesController keeps being pluralized.
All its 6 standard routes are listed:

Path	HTTP verb	Action	Behaviour
/profile	POST	create	Creates a new profile
/profile/new	GET	new	Returns the form a new profile
/profile	GET	show	Displays the profile for the accounted user
/profile	PUT	update	Updates the profile for the accounted user
/profile/edit	GET	edit	Returns the form for editing profile for the accounted user
/profile	DELETE	destroy	Deletes the profile for the accounted user (since the route is needless, it was removed from the standard routes)

Please compare the generated singular routes with their plural companions. Concluding singular resources simplify routing in dedicated cases.
Further articles of interest:

• REST in piece! ...a Ruby on Rails perspective
• Simple RESTful Ruby on Rails routes
• Reduce the routes! ... have as less as required

Supported by Ruby 2.1.1 and Ruby on Rails 3.2.17