在Json操作中创建的MVC 5 ViewModel，然后在发布模型中为null

Question

我有一个在我的JsonResult中创建的ViewModel，在操作结束时，我传递了我的视图模型return Json（VMpartnum，JsonRequestBehavior.AllowGet）;接下来，当我使用[httppost]单击按钮时，参数中的viewmodel为null。我的json中的所有内容都不存在。我如何将我的ViewModel从这个json传递到我的发布动作？我的猜测是我成功设置ajax的某种方式，但我不确定。

    $("#PartBook").on("change", function () {
                var selectV = $(this).val();
                var selectT = $(this).text();
                //var selected = $("#DDLpartbook option").prop("selected", true);
                //url: '/Parts/DoPartBookFunc?bookinfo=' + $(this).attr("value"),
                //alert("V " + selectV + "\nT " + selectT);
                //var option = $(this).find("option:selected").text();

                $.ajax({
                    url: '/Parts/DoPartBookFunc',
                    type: 'GET',
                    dataType: 'json',
                    data: { bookval: selectV },
                    //contentType: 'application/json; charset=utf-8',
                    success: function (data) {
                        //alert("s" + data.PartNextNumber);
                        $("#txtNextPart").val(data.PartNextNumber);
                    },
                    error: function (e) {
                        alert("e " + e.message);
                    }
                });
            });
public JsonResult DoPartBookFunc(int bookval)
        {
            var VMpartnum = new PartNumberViewModel();
            if(bookval != -1)
            {
                var book = context.PartBooks.Where(x => x.ID.Equals(bookval)).FirstOrDefault();
                if(book != null)
                {
                    var recordPartNumber = (from pnum in context.PartNumbers
                                            where pnum.PartGroup == book.Series
                                            orderby pnum.Last4Number descending
                                            select pnum).Take(10).ToList();

                    var recordPartBook = (from pbook in context.PartBooks
                                          where pbook.Series == book.Series                                          
                                          select pbook).FirstOrDefault();

                    var biggestPNumRecord = recordPartNumber.FirstOrDefault();
                    var nextEstimated = 0;
                    /* Load up my VIEWMODEL */
                    //VMpartnum.PartBook = biggestPNumRecord.PartGroup;
                    VMpartnum.PartBook = recordPartBook.Series;
                    VMpartnum.PartGroup = biggestPNumRecord.PartGroup;
                    VMpartnum.Last4Number = biggestPNumRecord.Last4Number;

                    if (biggestPNumRecord.Last4Number == "9999" || biggestPNumRecord.Last4Number == "-1")
                    {
                        TempData["Error"] = "Contact IT or Engineers 'Out of Part Numbers'";
                        //return RedirectToAction("TakeOutPart");
                    }
                    else
                    {
                        if(int.TryParse(biggestPNumRecord.Last4Number, out int last4plus1))
                        {
                            nextEstimated = last4plus1 + 1;

                            VMpartnum.PartNextNumber = VMpartnum.PartGroup + "." + nextEstimated;
                        }
                        else
                        {   // NOT INTEGER
                            try
                            {
                                //var nextNum = pnumRecord.Last4Number;
                                //nextEstimated = Convert.ToInt32(pnumRecord.Last4Number);

                                //VMpartnum.PartNextNumber = VMpartnum.PartGroup + "." + pnumRecord.Last4Number;
                                VMpartnum.PartNextNumber =  VMpartnum.PartNumber;
                            }
                            catch (Exception ex) { }

                        }                        
                        //var groupNum = biggestPNumRecord.PartGroup;
                        //ViewBag.NextPartNumber = groupNum + "." + nextEstimated;
                    }
                }
                else
                {
                    TempData["Error"] = "Couldn't find Partgroup|Series number";
                }
            }          
            //ViewBag.NextPartNumber = VMpartnum.PartNextNumber;

            return Json(VMpartnum, JsonRequestBehavior.AllowGet);
        }