Polymorphic URL helpers are methods for smart resolution to a named route call when given an Active Record model instance. They are to be used in combination with ActionController::Resources.

These methods are useful when you want to generate correct URL or path to a RESTful resource without having to know the exact type of the record in question.

Nested resources and/or namespaces are also supported, as illustrated in the example:

polymorphic_url([:admin, @article, @comment])

results in:

admin_article_comment_url(@article, @comment)

Usage within the framework

Polymorphic URL helpers are used in a number of places throughout the Rails framework:

  • url_for, so you can use it with a record as the argument, e.g. url_for(@article);

  • ActionView::Helpers::FormHelper uses polymorphic_path, so you can write form_for(@article) without having to specify :url parameter for the form action;

  • redirect_to (which, in fact, uses url_for) so you can write redirect_to(post) in your controllers;

  • ActionView::Helpers::AtomFeedHelper, so you don't have to explicitly specify URLs for feed entries.

Prefixed polymorphic helpers

In addition to polymorphic_url and polymorphic_path methods, a number of prefixed helpers are available as a shorthand to :action => "..." in options. Those are:

  • edit_polymorphic_url, edit_polymorphic_path

  • new_polymorphic_url, new_polymorphic_path

Example usage:

edit_polymorphic_path(@post)              # => "/posts/1/edit"
polymorphic_path(@post, :format => :pdf)  # => "/posts/1.pdf"

Using with mounted engines

If you use mounted engine, there is a possibility that you will need to use #polymorphic_url pointing at engine’s routes. To do that, just pass proxy used to reach engine’s routes as a first argument:

For example:

#polymorphic_url([blog, @post]) # it will call blog.post_path(@post) form_for([blog, @post]) # => "/blog/posts/1

Methods
P
Instance Public methods
polymorphic_path(record_or_hash_or_array, options = {})

Returns the path component of a URL for the given record. It uses polymorphic_url with :routing_type => :path.

Source: show | on GitHub 

# File actionpack/lib/action_dispatch/routing/polymorphic_routes.rb, line 132
def polymorphic_path(record_or_hash_or_array, options = {})
  polymorphic_url(record_or_hash_or_array, options.merge(:routing_type => :path))
end
polymorphic_url(record_or_hash_or_array, options = {})

Constructs a call to a named RESTful route for the given record and returns the resulting URL string. For example:

# calls post_url(post)
polymorphic_url(post) # => "http://example.com/posts/1"
polymorphic_url([blog, post]) # => "http://example.com/blogs/1/posts/1"
polymorphic_url([:admin, blog, post]) # => "http://example.com/admin/blogs/1/posts/1"
polymorphic_url([user, :blog, post]) # => "http://example.com/users/1/blog/posts/1"
polymorphic_url(Comment) # => "http://example.com/comments"

Options

  • :action - Specifies the action prefix for the named route: :new or :edit. Default is no prefix.

  • :routing_type - Allowed values are :path or :url. Default is :url.

Examples

# an Article record
polymorphic_url(record)  # same as article_url(record)

# a Comment record
polymorphic_url(record)  # same as comment_url(record)

# it recognizes new records and maps to the collection
record = Comment.new
polymorphic_url(record)  # same as comments_url()

# the class of a record will also map to the collection
polymorphic_url(Comment) # same as comments_url()

Source: show | on GitHub 

# File actionpack/lib/action_dispatch/routing/polymorphic_routes.rb, line 90
def polymorphic_url(record_or_hash_or_array, options = {})
  if record_or_hash_or_array.kind_of?(Array)
    record_or_hash_or_array = record_or_hash_or_array.compact
    if record_or_hash_or_array.first.is_a?(ActionDispatch::Routing::RoutesProxy)
      proxy = record_or_hash_or_array.shift
    end
    record_or_hash_or_array = record_or_hash_or_array[0] if record_or_hash_or_array.size == 1
  end

  record = extract_record(record_or_hash_or_array)
  record = record.to_model if record.respond_to?(:to_model)

  args = Array === record_or_hash_or_array ?
    record_or_hash_or_array.dup :
    [ record_or_hash_or_array ]

  inflection = if options[:action] && options[:action].to_s == "new"
    args.pop
    :singular
  elsif (record.respond_to?(:persisted?) && !record.persisted?)
    args.pop
    :plural
  elsif record.is_a?(Class)
    args.pop
    :plural
  else
    :singular
  end

  args.delete_if {|arg| arg.is_a?(Symbol) || arg.is_a?(String)}
  named_route = build_named_route_call(record_or_hash_or_array, inflection, options)

  url_options = options.except(:action, :routing_type)
  unless url_options.empty?
    args.last.kind_of?(Hash) ? args.last.merge!(url_options) : args << url_options
  end

  (proxy || self).send(named_route, *args)
end