Programming By Contract within a controller

widget_controller.rb

class WidgetsController < ApplicationController
  # ...
  # other functions
  #

  def create
    widget = Widget.new(params[:widget])
    widget.foo = some_thing
    widget.bar = some_other_thing
    widget.save!

    # It was successful
    respond_to do |format|
      format.html { redirect_to widgets_path, :notice => "Huzzah it works" }
    end
  rescue
    # Do your error handling here
    respond_to do |format|
      format.html { render :action => :new, :error  => "You are an idiot" }
    end
  end


end

This is a way for you to keep your error handling code separate from your main logic flow. It makes this super handy in rather complicated controllers. Granted you should be doing skinny controller and fat models, but there are cases where the controller will need to be a bit chubby

Now if you wanted to, you could just do

widget = Widget.create!(params[:widget])

but sometimes I need to set attributes that aren't attr_accessible

For more information on Exception handling, take a look at this:

http://blip.tv/avdi-grimm/exceptional-ruby-4778405