Quick tip - Flexible filters with respond_to

September 02 2006

Are you using filters in your controllers to pre-load objects and DRY up your actions? Take for example a RESTful customer controller. We know we want to load the customer record for the show, edit, update, and destroy actions and views.

class CustomersController < SecureController
  before_filter :find_customer, :except => [ :index, :new, :create ]
  
  ...
	
  private

    def find_customer
      @customer = Customer.find_by_id(params[:id])
    end

end

This works but is brittle. What happens when the filter can’t locate the customer? Should we display a flash message? What happens if this is an Ajax request? What if the call is through an API?

That’s where the following method can help…

def halt_and_respond_with(message)
  respond_to do |type|
    type.html do
      flash[:error] = message
      render :template => 'shared/message'          
    end
    type.js do
      render :update do |page|
        page.alert(message)
      end
    end
    type.xml { render :text => message }
  end
  false
end

Add this puppy to your application.rb and then refactor your filters like this:

class CustomersController < SecureController
  before_filter :find_customer, :except => [ :index, :new, :create ]

  ...

  private

    def find_customer
      @customer = Customer.find_by_id(params[:id])
      return halt_and_respond_with('Invalid customer.') if @customer.nil?
    end

end
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