Methods

Instance Public methods

rescue_from(*klasses, with: nil, &block)

Registers exception classes with a handler to be called by rescue_with_handler.

rescue_from receives a series of exception classes or class names, and an exception handler specified by a trailing :with option containing the name of a method or a Proc object. Alternatively, a block can be given as the handler.

Handlers that take one argument will be called with the exception, so that the exception can be inspected when dealing with it.

Handlers are inherited. They are searched from right to left, from bottom to top, and up the hierarchy. The handler of the first class for which exception.is_a?(klass) holds true is the one invoked, if any.

class ApplicationController < ActionController::Base
  rescue_from User::NotAuthorized, with: :deny_access # self defined exception
  rescue_from ActiveRecord::RecordInvalid, with: :show_errors

  rescue_from 'MyAppError::Base' do |exception|
    render xml: exception, status: 500
  end

  private
    def deny_access
      ...
    end

    def show_errors(exception)
      exception.record.new_record? ? ...
    end
end

Exceptions raised inside exception handlers are not propagated up.

📝 Source code 
# File activesupport/lib/active_support/rescuable.rb, line 51
      def rescue_from(*klasses, with: nil, &block)
        unless with
          if block_given?
            with = block
          else
            raise ArgumentError, "Need a handler. Pass the with: keyword argument or provide a block."
          end
        end

        klasses.each do |klass|
          key = if klass.is_a?(Module) && klass.respond_to?(:===)
            klass.name
          elsif klass.is_a?(String)
            klass
          else
            raise ArgumentError, "#{klass.inspect} must be an Exception class or a String referencing an Exception class"
          end

          # Put the new handler at the end because the list is read in reverse.
          self.rescue_handlers += [[key, with]]
        end
      end
🔎 See on GitHub

rescue_with_handler(exception, object: self, visited_exceptions: [])

Matches an exception to a handler based on the exception class.

If no handler matches the exception, check for a handler matching the (optional) exception.cause. If no handler matches the exception or its cause, this returns nil, so you can deal with unhandled exceptions. Be sure to re-raise unhandled exceptions if this is what you expect.

begin
  …
rescue => exception
  rescue_with_handler(exception) || raise
end

Returns the exception if it was handled and nil if it was not.

📝 Source code 
# File activesupport/lib/active_support/rescuable.rb, line 88
      def rescue_with_handler(exception, object: self, visited_exceptions: [])
        visited_exceptions << exception

        if handler = handler_for_rescue(exception, object: object)
          handler.call exception
          exception
        elsif exception
          if visited_exceptions.include?(exception.cause)
            nil
          else
            rescue_with_handler(exception.cause, object: object, visited_exceptions: visited_exceptions)
          end
        end
      end
🔎 See on GitHub