ActionDispatch::Routing::PolymorphicRoutes

# Action Dispatch Routing PolymorphicRoutes

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"