return the resource with the same persistence in cache

lib/cached_resource/caching.rb

@@ -81,7 +81,9 @@ def is_collection?(*arguments)
       # The key is processed to make sure it is valid.
       def cache_read(key)
         key = cache_key(Array(key)) unless key.is_a? String
-        object = cached_resource.cache.read(key).try(:dup)
+        object = cached_resource.cache.read(key).try do |cache|
+          cache.dup.tap { |o| o.instance_variable_set(:@persisted, cache.persisted?) if cache.respond_to?(:persisted?)}
+        end
         object && cached_resource.logger.info("#{CachedResource::Configuration::LOGGER_PREFIX} READ #{key}")
         object
       end
@@ -102,4 +104,4 @@ def cache_key(*arguments)
 
     end
   end
-end
+end

spec/cached_resource/caching_spec.rb

@@ -40,6 +40,12 @@ class Thing < ActiveResource::Base
       Thing.cached_resource.cache.read("thing/1").should == result
     end
 
+    it "should cache a response with the same persistence" do
+      result1 = Thing.find(1)
+      result2 = Thing.find(1)
+      result1.persisted?.should == result2.persisted?
+    end
+
     it "should read a response when the request is made again" do
       # make a request
       Thing.find(1)
@@ -266,4 +272,4 @@ class Thing < ActiveResource::Base
       new_result.name.should_not == old_result.name
     end
   end
-end
+end