How to update values in the database from the form

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ASP.NET

MySQL

This is my view file when i click update it has to be updated in database

myForm.attachEvent("onButtonClick", function (name, command) {
            if (name == "Update" && command == "Update") {     
                            $.ajax({
                    url: '/Home/Update',

                    data: JSON.stringify({
                        Id:myForm.getItemValue("Id"),
                        Name: myForm.getItemValue("Name"),
                        Duration: myForm.getItemValue("Duration"),
                        Year: myForm.getItemValue("Year"),
                        Comments: myForm.getItemValue("Comments")

                    }),
                    
                    cache: false,
                    dataType: "json",
                    success: function (str) {
                        alert(str.st);                    

                    },
                    type: 'POST',
                    contentType: 'application/json; charset=utf-8'
                });
            }
        });

In controller i define function for update

public JsonResult Update(int Id,string Name,int Duration,int Year,string Comments)
        {

            Training d = new Training();

            if (d.Id == Id)
            {
               d.Id=Id;
                d.Name = Name;
                d.Duration = Duration;
                d.Year = Year;
                d.Comments = Comments;
            }
                try
                {
                    this.dbContext.Add(d);
                    this.dbContext.SaveChanges();
                }
                catch
                {

                }

                var str = new { st = "successfully updated" };

                return Json(str, JsonRequestBehavior.AllowGet);
        }