always call `read_attribute` from the reader method

activerecord/lib/active_record/attribute_methods/read.rb

@@ -94,13 +94,7 @@ def cacheable_column?(column)
         end
 
         def internal_attribute_access_code(attr_name, cast_code)
-          method = instance_cast_method(attr_name)
-
-          if cache_attribute?(attr_name)
-            "cached_cast_attribute('#{attr_name}', :#{method})"
-          else
-            "cast_attribute('#{attr_name}', :#{method})"
-          end
+          "read_attribute('#{attr_name}') { |n| missing_attribute(n, caller) }"
         end
 
         def external_attribute_access_code(attr_name, cast_code)
@@ -125,14 +119,18 @@ def instance_cast_method(attr_name)
       # Returns the value of the attribute identified by <tt>attr_name</tt> after it has been typecast (for example,
       # "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)).
       def read_attribute(attr_name)
-        if @columns_hash.key? attr_name
-          if self.class.cache_attribute?(attr_name)
-            @attributes_cache[attr_name] ||= @columns_hash[attr_name].type_cast(@attributes[attr_name])
-          else
-            @columns_hash[attr_name].type_cast @attributes[attr_name]
-          end
+        column = @columns_hash.fetch(attr_name) {
+          return self.class.type_cast_attribute(attr_name, @attributes, @attributes_cache)
+        }
+
+        value = @attributes.fetch(attr_name) {
+          return block_given? ? yield(attr_name) : nil
+        }
+
+        if self.class.cache_attribute?(attr_name)
+          @attributes_cache[attr_name] ||= column.type_cast(value)
         else
-          self.class.type_cast_attribute(attr_name, @attributes, @attributes_cache)
+          column.type_cast value
         end
       end