Fixed generating namespaced table_name_prefix in engines

activerecord/lib/rails/generators/active_record/model/templates/module.rb

 <% module_namespacing do -%>
 module <%= class_path.map(&:camelize).join('::') %>
   def self.table_name_prefix
-    '<%= class_path.join('_') %>_'
+    '<%= namespaced? ? namespaced_class_path.join('_') : class_path.join('_') %>_'
   end
 end
 <% end -%>

railties/test/generators/namespaced_generators_test.rb

@@ -99,7 +99,7 @@ def test_model_with_namespace
     run_generator ["admin/account"]
     assert_file "app/models/test_app/admin.rb", /module TestApp/, /module Admin/
     assert_file "app/models/test_app/admin.rb", /def self\.table_name_prefix/
-    assert_file "app/models/test_app/admin.rb", /'admin_'/
+    assert_file "app/models/test_app/admin.rb", /'test_app_admin_'/
     assert_file "app/models/test_app/admin/account.rb", /module TestApp/, /class Admin::Account < ActiveRecord::Base/
   end