How to customize ids in URLs in your Rails app

Rails’ URL helpers allow you to pass in an Active Record object and it will automatically infer the proper URL including the id (e.g. link_to "Profile", @user). How can we get this behavior for custom objects? Custom objects Consider a custom Image class. We want URLs to look like /images/cat.gif. Rails relies on the to_param method to generate identifiers in URLs. If we define it on our custom object it can now be used with link_to just like ActiveRecord objects can. .