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])
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
edit_polymorphic_path(@post) # => "/posts/1/edit" polymorphic_path(@post, format: :pdf) # => "/posts/1.pdf"
Usage with mounted engines
If you are using a mounted engine and you need to use a polymorphic_url pointing at the engine’s routes, pass in the engine’s route proxy as the first argument to the method. For example:
polymorphic_url([blog, @post]) # calls blog.post_path(@post) form_for([blog, @post]) # => "/blog/posts/1"