02 Oct 2013 By: Greg Molnar

rescue_from is a very useful method in Rails. It lets us to catch exceptions and pass them to a callback or a block. A typical usecase is to handle ActiveRecord::RecordNotFound errors like in this example:

FooController < ActionController :: Base rescue_from ActiveRecord :: RecordNotFound , with : not_found private def notfound message = "Foo with ID #{ params [ :id ] } not found." logger . error message redirect_to not_found_url , info : message end end

In the example above whenever an ActiveRecord::RecordNotFound raised in the scope of the FooController it will be caught and the notfound method will log the event than redirect to the notfound page with a message to display in the browser. Since rescue_from works with a block too we can refactor the above as follows:

FooController < ActionController :: Base rescue_from ActiveRecord :: RecordNotFound do | exception | message = "Foo with ID #{ params [ :id ] } not found." logger . error message redirect_to not_found_url , info : message end end

Another case when rescue_from comes handy is when we use cancan for authorization and we want to handle the authorization errors. We can do so by add the following to the application controller:

rescue_from CanCan :: AccessDenied do | exception | redirect_to root_url , :alert => exception . message end

As you see in this case we display the exception message set by cancan. If you want to use rescue_from from in a class which does not inherit from ActionController::Base you just need to mixin the ActiveSupport::Rescuable :