keep a cache of the reader methods so we can reuse them

activerecord/lib/active_record/attribute_methods.rb

@@ -28,6 +28,54 @@ def self.set_name_cache(name, value)
       end
     }
 
+    ReaderMethodCache = Class.new {
+      include Mutex_m
+
+      def initialize
+        super
+        @module = Module.new
+        @method_cache = {}
+      end
+
+      # We want to generate the methods via module_eval rather than
+      # define_method, because define_method is slower on dispatch.
+      # Evaluating many similar methods may use more memory as the instruction
+      # sequences are duplicated and cached (in MRI).  define_method may
+      # be slower on dispatch, but if you're careful about the closure
+      # created, then define_method will consume much less memory.
+      #
+      # But sometimes the database might return columns with
+      # characters that are not allowed in normal method names (like
+      # 'my_column(omg)'. So to work around this we first define with
+      # the __temp__ identifier, and then use alias method to rename
+      # it to what we want.
+      #
+      # We are also defining a constant to hold the frozen string of
+      # the attribute name. Using a constant means that we do not have
+      # to allocate an object on each call to the attribute method.
+      # Making it frozen means that it doesn't get duped when used to
+      # key the @attributes_cache in read_attribute.
+      def [](name)
+        synchronize do
+          @method_cache.fetch(name) {
+            safe_name = name.unpack('h*').first
+            temp_method = "__temp__#{safe_name}"
+
+            ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
+
+            @module.module_eval <<-STR, __FILE__, __LINE__ + 1
+              def #{temp_method}
+                name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{safe_name}
+                read_attribute(name) { |n| missing_attribute(n, caller) }
+              end
+            STR
+
+            @method_cache[name] = @module.instance_method temp_method
+          }
+        end
+      end
+    }.new
+
     module ClassMethods
       def inherited(child_class) #:nodoc:
         child_class.initialize_generated_modules

activerecord/lib/active_record/attribute_methods/read.rb

@@ -32,41 +32,9 @@ def cache_attribute?(attr_name)
 
         protected
 
-        # We want to generate the methods via module_eval rather than
-        # define_method, because define_method is slower on dispatch.
-        # Evaluating many similar methods may use more memory as the instruction
-        # sequences are duplicated and cached (in MRI).  define_method may
-        # be slower on dispatch, but if you're careful about the closure
-        # created, then define_method will consume much less memory.
-        #
-        # But sometimes the database might return columns with
-        # characters that are not allowed in normal method names (like
-        # 'my_column(omg)'. So to work around this we first define with
-        # the __temp__ identifier, and then use alias method to rename
-        # it to what we want.
-        #
-        # We are also defining a constant to hold the frozen string of
-        # the attribute name. Using a constant means that we do not have
-        # to allocate an object on each call to the attribute method.
-        # Making it frozen means that it doesn't get duped when used to
-        # key the @attributes_cache in read_attribute.
         def define_method_attribute(name)
-          safe_name = name.unpack('h*').first
-          temp_method = "__temp__#{safe_name}"
-
-          ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
-
-          generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
-            def #{temp_method}
-              name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{safe_name}
-              read_attribute(name) { |n| missing_attribute(n, caller) }
-            end
-          STR
-
-          generated_attribute_methods.module_eval do
-            alias_method name, temp_method
-            undef_method temp_method
-          end
+          method = ActiveRecord::AttributeMethods::ReaderMethodCache[name]
+          generated_attribute_methods.module_eval { define_method name, method }
         end
 
         private