update caching guide: stale? can also figure out last_modified on its own

1 files changed, 12 insertions, 1 deletions

diff --git a/guides/source/caching_with_rails.textile b/guides/source/caching_with_rails.textile
index f6d6c8b550..9f1ac18814 100644
--- a/guides/source/caching_with_rails.textile
+++ b/guides/source/caching_with_rails.textile
@@ -439,7 +439,7 @@ class ProductsController < ApplicationController
 
     # If the request is stale according to the given timestamp and etag value
     # (i.e. it needs to be processed again) then execute this block
-    if stale?(:last_modified => @product.updated_at.utc, :etag => @product)
+    if stale?(:last_modified => @product.updated_at.utc, :etag => @product.cache_key)
       respond_to do |wants|
         # ... normal response processing
       end
@@ -453,6 +453,17 @@ class ProductsController < ApplicationController
 end
 </ruby>
 
+Instead of a options hash, you can also simply pass in a model, Rails will use the methods +updated_at+ and +cache_key+ for setting +last_modified+ and +etag+:
+
+<ruby>
+class ProductsController < ApplicationController
+  def show
+    @product = Product.find(params[:id])
+    respond_with(@product) if stale?(@product)
+  end
+end
+</ruby>
+
 If you don't have any special response processing and are using the default rendering mechanism (i.e. you're not using respond_to or calling render yourself) then you’ve got an easy helper in fresh_when:
 
 <ruby>