1 files changed, 11 insertions, 12 deletions
diff --git a/activemodel/lib/active_model/naming.rb b/activemodel/lib/active_model/naming.rb
index 8cf1a191f4..1f1749af4e 100644
--- a/activemodel/lib/active_model/naming.rb
+++ b/activemodel/lib/active_model/naming.rb
@@ -1,5 +1,7 @@
 require 'active_support/core_ext/hash/except'
 require 'active_support/core_ext/module/introspection'
+require 'active_support/core_ext/module/remove_method'
+require 'active_support/core_ext/module/delegation'
 
 module ActiveModel
   class Name
@@ -129,7 +131,7 @@ module ActiveModel
     #
     # Equivalent to +to_s+.
     delegate :==, :===, :<=>, :=~, :"!~", :eql?, :to_s,
-             :to_str, to: :name
+             :to_str, :as_json, to: :name
 
     # Returns a new ActiveModel::Name instance. By default, the +namespace+
     # and +name+ option will take the namespace and name of the given class
@@ -189,8 +191,8 @@ module ActiveModel
 
     private
 
-    def _singularize(string, replacement='_')
-      ActiveSupport::Inflector.underscore(string).tr('/', replacement)
+    def _singularize(string)
+      ActiveSupport::Inflector.underscore(string).tr('/', '_')
     end
   end
 
@@ -211,13 +213,12 @@ module ActiveModel
   #   BookModule::BookCover.model_name.i18n_key  # => :"book_module/book_cover"
   #
   # Providing the functionality that ActiveModel::Naming provides in your object
-  # is required to pass the Active Model Lint test. So either extending the
+  # is required to pass the \Active \Model Lint test. So either extending the
   # provided method below, or rolling your own is required.
   module Naming
     def self.extended(base) #:nodoc:
-      base.class_eval do
-        delegate :model_name, to: :class
-      end
+      base.remove_possible_method :model_name
+      base.delegate :model_name, to: :class
     end
 
     # Returns an ActiveModel::Name object for module. It can be
@@ -305,12 +306,10 @@ module ActiveModel
     end
 
     def self.model_name_from_record_or_class(record_or_class) #:nodoc:
-      if record_or_class.respond_to?(:model_name)
-        record_or_class.model_name
-      elsif record_or_class.respond_to?(:to_model)
-        record_or_class.to_model.class.model_name
+      if record_or_class.respond_to?(:to_model)
+        record_or_class.to_model.model_name
       else
-        record_or_class.class.model_name
+        record_or_class.model_name
       end
     end
     private_class_method :model_name_from_record_or_class