version numbers

README.markdown

@@ -79,6 +79,15 @@ With a limit attribute, indices will only store limit + buffer in the cache. As
 
 `Message.count(:all, :conditions => {:sender_id => ...})` will use the cache rather than the database. This happens for "free" -- no additional declarations are necessary.
 
+### Version Numbers ###
+
+    class User
+      version 7
+      index ...
+    end
+
+You can increment the version number as you migrate your schema.
+
 ### Transactions ###
 
 Because of the parallel requests writing to the same indices, race conditions are possible. We have created a pessimistic "transactional" memcache client to handle the locking issues.
@@ -136,7 +145,6 @@ Sometimes your code will request the same cache key twice in one request. You ca
 #### Step 1: `config/initializers/cache_money.rb` ####
 
 Place this in `config/initializers/cache_money.rb`
-
     require 'cache_money'
 
     config = YAML.load(IO.read(File.join(RAILS_ROOT, "config", "memcache.yml")))[RAILS_ENV]

lib/cash/accessor.rb

@@ -66,7 +66,7 @@ def expire(key)
       end
 
       def cache_key(key)
-        "#{name}/#{key.to_s.gsub(' ', '+')}"
+        "#{name}:#{cache_config.version}/#{key.to_s.gsub(' ', '+')}"
       end
     end
 

lib/cash/config.rb

@@ -10,6 +10,7 @@ def self.included(a_module)
     module ClassMethods
       def self.extended(a_class)
         class << a_class
+          attr_reader :cache_config
           delegate :repository, :indices, :to => :@cache_config
           alias_method_chain :inherited, :cache_config
         end
@@ -25,6 +26,10 @@ def index(attributes, options = {})
         (@cache_config.indices.unshift(Index.new(@cache_config, self, attributes, options))).uniq!
       end
 
+      def version(number)
+        @cache_config.options[:version] = number
+      end
+
       def cache_config=(config)
         @cache_config = config
       end
@@ -50,6 +55,10 @@ def ttl
         @options[:ttl]
       end
 
+      def version
+        @options[:version] || 1
+      end
+
       def indices
         @indices ||= active_record == ActiveRecord::Base ? [] : [Index.new(self, active_record, active_record.primary_key)]
       end

spec/cash/accessor_spec.rb

@@ -22,8 +22,8 @@ module Cash
         describe 'when there is a total cache miss' do
           it 'yields the keys to the block' do
             Story.fetch(["yabba", "dabba"]) { |*missing_ids| ["doo", "doo"] }.should == {
-              "Story/yabba" => "doo",
-              "Story/dabba" => "doo"
+              "Story:1/yabba" => "doo",
+              "Story:1/dabba" => "doo"
             }
           end
         end
@@ -32,8 +32,8 @@ module Cash
           it 'yields just the missing ids to the block' do
             Story.set("yabba", "dabba")
             Story.fetch(["yabba", "dabba"]) { |*missing_ids| "doo" }.should == {
-              "Story/yabba" => "dabba",
-              "Story/dabba" => "doo"
+              "Story:1/yabba" => "dabba",
+              "Story:1/dabba" => "doo"
             }
           end
         end
@@ -145,5 +145,15 @@ module Cash
         end
       end
     end
+
+    describe '#cache_key' do
+      it 'uses the version number' do
+        Story.version 1
+        Story.cache_key("foo").should == "Story:1/foo"
+
+        Story.version 2
+        Story.cache_key("foo").should == "Story:2/foo"
+      end
+    end
   end
 end