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 the 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"

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"
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