[Fix #30] FeatureCaching: cache nils as :NO_SUCH_FEATURE to avoid re-…

…reads

lib/arturo/feature_caching.rb

@@ -16,6 +16,10 @@ module Arturo
   # to use a shared cache like Memcached.
   module FeatureCaching
 
+    # A marker in the cache to record the fact that the feature with the
+    # given symbol doesn't exist.
+    NO_SUCH_FEATURE = :NO_SUCH_FEATURE
+
     def self.extended(base)
       class <<base
         alias_method_chain :to_feature, :caching
@@ -37,10 +41,12 @@ def to_feature_with_caching(feature_or_symbol)
         feature_cache.write(feature_or_symbol.symbol.to_sym, feature_or_symbol, :expires_in => cache_ttl)
         feature_or_symbol
       elsif (cached_feature = feature_cache.read(feature_or_symbol.to_sym))
-        cached_feature
-      elsif (f = to_feature_without_caching(feature_or_symbol))
-        feature_cache.write(f.symbol.to_sym, f, :expires_in => cache_ttl)
-        f
+        cached_feature == NO_SUCH_FEATURE ? nil : cached_feature
+      else
+        symbol = feature_or_symbol.to_sym
+        feature = to_feature_without_caching(symbol) || NO_SUCH_FEATURE
+        feature_cache.write(symbol, feature, :expires_in => cache_ttl)
+        feature
       end
     end
 

test/dummy_app/test/unit/cache_test.rb

@@ -42,6 +42,13 @@ def test_subsequent_loads_within_ttl_hit_cache
     Arturo::Feature.to_feature(@feature.symbol)
   end
 
+  def test_nils_are_cached
+    Arturo::Feature.expects(:where).once.returns([])
+    Arturo::Feature.to_feature(:ramen)
+    Arturo::Feature.to_feature(:ramen)
+    Arturo::Feature.to_feature(:ramen)
+  end
+
   def test_works_with_other_cache_backend
     Arturo::Feature.feature_cache = StupidCache.new
     Arturo::Feature.expects(:where).once.returns([@feature.reload])