Singular or plural controller and helper names in Rails

Question

Definitely plural.

With restful routing and a singular controller

Controller:

dog_controller.rb  

Routes:

map.resources :dogs  # => blows up  
map.resources :dog  # is ok, but...  
dogs_path # => blows up  
dog_path  # => ok  

Using a plural controller

Controller:

dogs_controller.rb

Routes:

map.resources :dogs  
dogs_path # => ok  
dog_path # => ok  

rails generate controller --help has plural examples:

Example:
`rails generate controller CreditCards open debit credit close`

CreditCards controller with URLs like /credit_cards/debit.
    Controller: app/controllers/credit_cards_controller.rb
    Test:       test/controllers/credit_cards_controller_test.rb
    Views:      app/views/credit_cards/debit.html.erb [...]
    Helper:     app/helpers/credit_cards_helper.rb

Using plural names for controllers is just a convention.

Plural names usually sound more natural (especially for controllers that are tied directly to a specific model: User -> Users, etc.), but you can use whatever you want.

As for helpers, all helpers are available for all controllers by default, so technically, how you name your helpers doesn't matter at all. It's just another convention to keep a controller's helper functions in a helper with the same name as the controller.

A Model is singular because it references a single object like User. A controller is plural because it is the controls (methods) for the collection of Users. How one names the routes is all up to that individual developer. I've never had a user complain that a URL for a web request is singular or plural. The end result to maintain a common convention for current and future contributors while serving quality page displays or the API requests for the end users.

You have a very complete explanation in the Rails guides: http://edgeguides.rubyonrails.org/routing.html#resource-routing-the-rails-default

It is the Rails convention that one controller handles one model, whether one or more instances of that model can exist during runtime. However, you can have a Rails application where (some of) the controllers (and the associated views) are not associated with any particular model, but rather handle a more complex set of functionality. In this case, the automatic pluralization doesn't make any sense.

The Rails application I'm currently working on fits into this category, and it's simply an irritation to me that Rails expects that the identifiers I define as a singular in one place are then used in their plural forms in other places. For example, I might want to define something like this in config/routes.rb:

  resource :dashboard, :only => [:show]

and then I want a controller DashboardController to display summary information about certain aspects of the application, gathering information from more than one database table. So here, Dashboard does not refer to any model of the application, and it would be just weird to have the controller's name be DashboardsController.

I found a good solution to the irritation of automatic pluralization in this answer. In short, edit file config/initializers/inflections.rb and add the words you don't want to be automatically pluralized to this definition:

ActiveSupport::Inflector.inflections do |inflect|
  inflect.uncountable %w( dashboard foo bar baz )
end