matthooks · November 20, 2011 02:58 · Nov 20, 2011
diff --git a/gistfile1.rb b/gistfile1.rb
@@ -0,0 +1,30 @@
+module CounterCache
+  extend ActiveSupport::Concern
+
+  module ClassMethods
+    def counter_cache(field)
+      class_eval <<-EOF
+        after_create "increment_counter_for_#{field}"
+        after_destroy "decrement_counter_for_#{field}"
+      EOF
+    end
+  end
+
+  module InstanceMethods
+    def method_missing(method, *args)
+      if matches = method.to_s.match(/^(in|de)crement_counter_for_(.*)$/) then
+        dir = matches[1] == "in" ? 1 : -1
+        parent_association = matches[2]
+
+        if parent = self.send(parent_association) then
+          name = "#{self.class.collection_name}_count"
+          if parent.respond_to?(name)
+            parent.increment(name => dir)
+          end
+        end
+      else
+        super
+      end
+    end
+  end
+end