Change ModuleAppTag into "Module name"Tag.

app/controllers/admin/tags_controller.rb

@@ -19,7 +19,12 @@ class Admin::TagsController < ApplicationController
   end
 
   def create
-    @tag = (params[:tag][:module_app_id].blank? ? Tag.create(params[:tag]) : ModuleAppTag.create(params[:tag]))
+    if params[:tag][:module_app_id].blank?
+      @tag = Tag.create(params[:tag])
+    else
+      module_app = ModuleApp.find(params[:tag][:module_app_id])
+      @tag = eval("#{module_app.key.capitalize}Tag").create(params[:tag])
+    end
   end
 
   def update