eagerly assign the attribute name cache, remove const_missing

activerecord/lib/active_record/attribute_methods.rb

@@ -30,8 +30,11 @@ def initialize_generated_modules # :nodoc:
           extend Mutex_m
 
           const_set :AttrNames, Module.new {
-            def self.const_missing(name)
-              const_set(name, [name.to_s.sub(/ATTR_/, '')].pack('h*').freeze)
+            def self.set_name_cache(name, value)
+              const_name = "ATTR_#{name}"
+              unless const_defined? const_name
+                const_set const_name, value
+              end
             end
           }
         }

activerecord/lib/active_record/attribute_methods/read.rb

@@ -49,6 +49,8 @@ def cache_attribute?(attr_name)
         # key the @attributes_cache in read_attribute.
         def define_method_attribute(name)
           safe_name = name.unpack('h*').first
+          generated_attribute_methods::AttrNames.set_name_cache safe_name, name
+
           generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
             def __temp__#{safe_name}
               read_attribute(AttrNames::ATTR_#{safe_name}) { |n| missing_attribute(n, caller) }

activerecord/lib/active_record/attribute_methods/write.rb

@@ -14,6 +14,8 @@ module ClassMethods
         # this code.
         def define_method_attribute=(name)
           safe_name = name.unpack('h*').first
+          generated_attribute_methods::AttrNames.set_name_cache safe_name, name
+
           generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
             def __temp__#{safe_name}=(value)
               write_attribute(AttrNames::ATTR_#{safe_name}, value)