1 files changed, 90 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb b/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb
new file mode 100644
index 0000000000..42ff1d7d54
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb
@@ -0,0 +1,90 @@
+module ActiveRecord
+  module ConnectionAdapters # :nodoc:
+    module QueryCache
+      class << self
+        def included(base)
+          base.class_eval do
+            attr_accessor :query_cache_enabled
+            alias_method_chain :columns, :query_cache
+            alias_method_chain :select_all, :query_cache
+          end
+
+          dirties_query_cache base, :insert, :update, :delete
+        end
+
+        def dirties_query_cache(base, *method_names)
+          method_names.each do |method_name|
+            base.class_eval <<-end_code, __FILE__, __LINE__
+              def #{method_name}_with_query_dirty(*args)
+                clear_query_cache if @query_cache_enabled
+                #{method_name}_without_query_dirty(*args)
+              end
+
+              alias_method_chain :#{method_name}, :query_dirty
+            end_code
+          end
+        end
+      end
+
+      # Enable the query cache within the block.
+      def cache
+        old, @query_cache_enabled = @query_cache_enabled, true
+        @query_cache ||= {}
+        yield
+      ensure
+        clear_query_cache
+        @query_cache_enabled = old
+      end
+
+      # Disable the query cache within the block.
+      def uncached
+        old, @query_cache_enabled = @query_cache_enabled, false
+        yield
+      ensure
+        @query_cache_enabled = old
+      end
+
+      def clear_query_cache
+        @query_cache.clear if @query_cache
+      end
+
+      def select_all_with_query_cache(*args)
+        if @query_cache_enabled
+          cache_sql(args.first) { select_all_without_query_cache(*args) }
+        else
+          select_all_without_query_cache(*args)
+        end
+      end
+
+      def columns_with_query_cache(*args)
+        if @query_cache_enabled
+          @query_cache["SHOW FIELDS FROM #{args.first}"] ||= columns_without_query_cache(*args)
+        else
+          columns_without_query_cache(*args)
+        end
+      end
+
+      private
+        def cache_sql(sql)
+          result =
+            if @query_cache.has_key?(sql)
+              log_info(sql, "CACHE", 0.0)
+              @query_cache[sql]
+            else
+              @query_cache[sql] = yield
+            end
+
+          case result
+          when Array
+            result.collect { |row| row.dup }
+          when nil, Fixnum, Float, true, false
+            result
+          else
+            result.dup
+          end
+        rescue TypeError
+          result
+        end
+    end
+  end
+end