Rescue exceptions raised in controller actions.

rescue_from receives a series of exception classes or class names, and a trailing :with option with the name of a method or a Proc object to be called to handle them. Alternatively a block can be given.

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

protected
  def deny_access
    ...
  end

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

end

Source Code

# File action_controller/rescue.rb, line 88
def rescue_from(*klasses, &block)
  options = klasses.extract_options!
  unless options.has_key?(:with)
    block_given? ? options[:with] = block : raise(ArgumentError, "Need a handler. Supply an options hash that has a :with key as the last argument.")
  end

  klasses.each do |klass|
    key = if klass.is_a?(Class) && klass <= Exception
      klass.name
    elsif klass.is_a?(String)
      klass
    else
      raise(ArgumentError, "#{klass} is neither an Exception nor a String")
    end

    # Order is important, we put the pair at the end. When dealing with an
    # exception we will follow the documented order going from right to left.
    rescue_handlers << [key, options[:with]]
  end
end