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
resources :posts

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

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

  redirect_to(post) # Calls polymorphic_url(post) which in turn calls post_url(post)
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 expect that same naming convention and allows you to write less code if you follow it.

Methods
D
R
S
Constants
JOIN = '_'.freeze
 
NEW = 'new'.freeze
 
Instance Public 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"

Source: show | on GitHub 

# File actionpack/lib/action_controller/record_identifier.rb, line 42
def dom_class(record_or_class, prefix = nil)
  singular = ActiveModel::Naming.param_key(record_or_class)
  prefix ? "#{prefix}#{JOIN}#{singular}" : singular
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"

Source: show | on GitHub 

# File actionpack/lib/action_controller/record_identifier.rb, line 56
def dom_id(record, prefix = nil)
  if record_id = record_key_for_dom_id(record)
    "#{dom_class(record, prefix)}#{JOIN}#{record_id}"
  else
    dom_class(record, prefix || NEW)
  end
end
Instance Protected methods
record_key_for_dom_id(record)

Returns a string representation of the key attribute(s) that is suitable for use in an HTML DOM id. This can be overwritten to customize the default generated string representation if desired. If you need to read back a key from a #dom_id in order to query for the underlying database record, you should write a helper like ‘person_record_from_dom_id’ that will extract the key either based on the default implementation (which just joins all key attributes with ‘_’) or on your own overwritten version of the method. By default, this implementation passes the key string through a method that replaces all characters that are invalid inside DOM ids, with valid ones. You need to make sure yourself that your dom ids are valid, in case you overwrite this method.

Source: show | on GitHub 

# File actionpack/lib/action_controller/record_identifier.rb, line 74
def record_key_for_dom_id(record)
  record = record.to_model if record.respond_to?(:to_model)
  key = record.to_key
  key ? sanitize_dom_id(key.join('_')) : key
end
sanitize_dom_id(candidate_id)

Replaces characters that are invalid in HTML DOM ids with valid ones.

Source: show | on GitHub 

# File actionpack/lib/action_controller/record_identifier.rb, line 81
def sanitize_dom_id(candidate_id)
  candidate_id # TODO implement conversion to valid DOM id values
end