How to resolve this error

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entity-framework

{"Unable to update the EntitySet 'Addons' because it has a DefiningQuery and no <insertfunction> element exists in the <modificationfunctionmapping> element to support the current operation."}

[HttpPost]
       [ValidateInput(false)]
       public ActionResult AddAddon(AddonModel addmodel)
       {

           if(ModelState.IsValid)
           {
               Addon addonobj = new Addon();
               addonobj.AddonTitle = addmodel.AddonTitle;
               addonobj.Price = addmodel.Price ?? 0;
               addonobj.Description = addmodel.Description;
               addonobj.Status = true;
               addonobj.CreatedDate = addmodel.CreatedDate;
               addonobj.UpdatedDate = addmodel.UpdatedDate;
               snw.Addons.Add(addonobj);
               snw.SaveChanges();
               return RedirectToAction("List");
           }

           return View();
       }