The record identifier encapsulates a number of naming conventions for dealing with records, like Active Records or Active Resources or pretty much any other model type that has an id. These patterns are then used to try elevate the view actions to a higher logical level. Example:

  # routes
  map.resources :posts

  # view
  <% div_for(post) do %>     <div id="post_45" class="post">
    <%= post.body %>           What a wonderful world!
  <% end %>                  </div>

  # controller
  def destroy
    post = Post.find(params[:id])
    post.destroy

    respond_to do |format|
      format.html { redirect_to(post) } # Calls polymorphic_url(post) which in turn calls post_url(post)
      format.js do
        # Calls: new Effect.fade('post_45');
        render(:update) { |page| page[post].visual_effect(:fade) }
      end
    end
  end

As the example above shows, you can stop caring to a large extent what the actual id of the post is. You just know that one is being assigned and that the subsequent calls in redirect_to and the RJS expect that same naming convention and allows you to write less code if you follow it.

Methods
Constants
JOIN = '_'.freeze
NEW = 'new'.freeze
Public Instance methods
dom_class(record_or_class, prefix = nil)

The DOM class convention is to use the singular form of an object or class. Examples:

  dom_class(post)   # => "post"
  dom_class(Person) # => "person"

If you need to address multiple instances of the same class in the same view, you can prefix the dom_class:

  dom_class(post, :edit)   # => "edit_post"
  dom_class(Person, :edit) # => "edit_person"
    # File actionpack/lib/action_controller/record_identifier.rb, line 61
61:     def dom_class(record_or_class, prefix = nil)
62:       singular = singular_class_name(record_or_class)
63:       prefix ? "#{prefix}#{JOIN}#{singular}" : singular
64:     end
dom_id(record, prefix = nil)

The DOM id convention is to use the singular form of an object or class with the id following an underscore. If no id is found, prefix with "new_" instead. Examples:

  dom_id(Post.find(45))       # => "post_45"
  dom_id(Post.new)            # => "new_post"

If you need to address multiple instances of the same class in the same view, you can prefix the dom_id:

  dom_id(Post.find(45), :edit) # => "edit_post_45"
    # File actionpack/lib/action_controller/record_identifier.rb, line 75
75:     def dom_id(record, prefix = nil) 
76:       if record_id = record.id
77:         "#{dom_class(record, prefix)}#{JOIN}#{record_id}"
78:       else
79:         dom_class(record, prefix || NEW)
80:       end
81:     end
partial_path(record_or_class, controller_path = nil)

Returns plural/singular for a record or class. Example:

  partial_path(post)                   # => "posts/post"
  partial_path(Person)                 # => "people/person"
  partial_path(Person, "admin/games")  # => "admin/people/person"
    # File actionpack/lib/action_controller/record_identifier.rb, line 42
42:     def partial_path(record_or_class, controller_path = nil)
43:       name = model_name_from_record_or_class(record_or_class)
44: 
45:       if controller_path && controller_path.include?("/")
46:         "#{File.dirname(controller_path)}/#{name.partial_path}"
47:       else
48:         name.partial_path
49:       end
50:     end
plural_class_name(record_or_class)

Returns the plural class name of a record or class. Examples:

  plural_class_name(post)             # => "posts"
  plural_class_name(Highrise::Person) # => "highrise_people"
    # File actionpack/lib/action_controller/record_identifier.rb, line 87
87:     def plural_class_name(record_or_class)
88:       model_name_from_record_or_class(record_or_class).plural
89:     end
singular_class_name(record_or_class)

Returns the singular class name of a record or class. Examples:

  singular_class_name(post)             # => "post"
  singular_class_name(Highrise::Person) # => "highrise_person"
    # File actionpack/lib/action_controller/record_identifier.rb, line 95
95:     def singular_class_name(record_or_class)
96:       model_name_from_record_or_class(record_or_class).singular
97:     end