我的jQuery ajax函数总是返回错误，此错误消息为（常规故障）

我试图使用mvc中的另一个下拉列表绑定下拉列表中的数据。 当我从类别中选择时，子类别在控制器中的jsonresult操作中返回一个值，但ajax给了我一个错误General Failure，我不知道错误在哪里

这是控制中的代码

        public ActionResult Create()
    {
        List<sub_categories> subCategoryList = new List<sub_categories>();

        // Select List Category
        var dropdownListCategoryEnr = new SelectList(db.category.ToList(), "cat_id", "cat_name_en");
        ViewBag.cat_id = dropdownListCategoryEnr;

        //Select List Sub category
        ViewBag.sub_cat_id = new SelectList(subCategoryList, "sub_cat_id", "sub_name_en");

        return View();
    }

    [HttpGet]
    public JsonResult GetSubCategoryById(string categoryId = "")
    {
        List<sub_categories> subCategoryList = new List<sub_categories>();
        int ID = 0;
        if(int.TryParse(categoryId, out ID))
        {
            subCategoryList = db.sub_categories.Where(x => x.cat_id.Equals(ID) && x.is_deleted == false).ToList();
        }

        if(Request.IsAjaxRequest())
        {
            return new JsonResult
            {
                Data = subCategoryList,
                JsonRequestBehavior = JsonRequestBehavior.AllowGet
            };
        }
        else
        {
            return new JsonResult
            {
                Data = "Not Valid request",
                JsonRequestBehavior = JsonRequestBehavior.AllowGet
            };
        }
    }

这是jquery代码：-

$(document).ready(function () {
            $("#cat_id").change(function () {
                // this will call when Country Dropdown select change
                var categoryId = parseInt($("#cat_id").val());
                if (!isNaN(categoryId)) {
                    var ddsub = $("#sub_cat_id");
                    ddsub.empty(); // this line is for clear all items from State dropdown
                    ddsub.append($("<option></option").val("").html("Select State"));

                    // Here I will call Controller Action via Jquery to load State for selected Country
                    $.ajax({
                        url: "@Url.Action("GetSubCategoryById", "Products")",
                        type: "GET",
                        data: { categoryId: categoryId },
                        dataType: "json",
                        success: function (data) {
                            $.each(data, function (i, val) {
                                ddsub.append(
                                        $("<option></option>").val(val.sub_cat_id).html(val.sub_name_en)
                                    );
                            });
                        },
                        error: function (xhr, ajaxOptions, errorThrown) {
                            alert(xhr.responseText);
                        }
                    });
                }
            });
        });

试试看

if (Request.IsAjaxRequest())
{
    return Json(subCategoryList, JsonRequestBehavior.AllowGet);
}
else
{
    return Json("Not Valid Request", JsonRequestBehavior.AllowGet);
}

---

我创建了一个类似的示例，其中根据父下拉列表中选择的值填充下拉列表。请试一试

<div class="box box-frame" style="padding-bottom: 10px;">
        <div class="box-inner" style="padding-left: 0px">
            <div class="box-caption">Search Reports</div>
            <div style="padding: 2px;">
                @Html.ValidationSummary()
            </div>
            <ul class="piped font-weight-normal">
                <li>
                    <b>Company: </b>

                            @Html.DropDownListFor(m =>  Model.CompanyId,
                                                        Model.CompanyLookupValues.Select(
                                                            c => new SelectListItem() { Value = c.CompanyId.ToString(), Text = c.CompanyName }
                                                        ),
                                                         "-- select --",
                                                        new { @class = "width-4",onchange = "GetReportTypes();" })
                            @Html.ValidationMessageFor(m => Model.CompanyId)
                            <text>&nbsp;&nbsp;</text>

                    <b> Report Type: </b>
                     @Html.DropDownListFor(m => Model.ReportId,
                              Model.ReportLookupValues.Select(c => new SelectListItem() { Value = c.ReportId.ToString(), Text = c.ReportName }),
                                "-- select --",
                            new { @class = "width-4" })
                        @Html.ValidationMessageFor(m => Model.ReportId)
                        &nbsp;&nbsp;
                         <input class="button-primary" type="button" id="btnGetReportFilters" value="&nbsp;&nbsp;Get Report Filters&nbsp;&nbsp;" onclick="GetReportFilters();" />
                </li>
            </ul>

        </div>`enter code here`
    </div>

Jquery代码

        function GetReportTypes() {
                var companyId = $("#CompanyId").val();
                if (companyId != '') {
                    var url = '@Url.Action("GetReportTypes", "Report")';
                    $.getJSON(url + '?companyId=' + companyId, function (data) {
                        var select = $("#ReportId");
                        select.empty();
                        select.append($('<option/>', {
                            value: '',
                            text: "-- select --"
                        }));

                        $.each(data, function (index, itemData) {
                            select.append($('<option/>', {
                                value: itemData.ReportId,
                                text: itemData.ReportName
                            }));
                        });
                    });
                }
            }

MVC代码

    public JsonResult GetReportTypes(int companyId)
        {
            List<Report> reportTypes = new List<Report>();
            if (companyId > 0)
            {
                // for admin, return all report types
                if (IsAdministrator)
                {
                    reportTypes = ReferenceDataService.GetReportTypes(true).Select(r => new Report { ReportId = r.ReportId, ReportName = r.ReportName }).ToList();
                }
                else
                {

                            reportTypes = ReferenceDataService.GetReportTypes(false).Select(r => new Report { ReportId = r.ReportId, ReportName = r.ReportName }).ToList();
                }


            }

            return Json(reportTypes, JsonRequestBehavior.AllowGet); ;

        }

---

添加此行时：-db.Configuration.ProxyCreationEnabled=false；很好，为什么伙计们，这行代码用的是什么？

当您提出AJAX请求时，您应该能够在Chrome developer tools F12中检查它，这可能会显示错误消息。这里没有任何错误subCateogryList给我值，但AJAX代码给我一般的失败

    public JsonResult GetReportTypes(int companyId)
        {
            List<Report> reportTypes = new List<Report>();
            if (companyId > 0)
            {
                // for admin, return all report types
                if (IsAdministrator)
                {
                    reportTypes = ReferenceDataService.GetReportTypes(true).Select(r => new Report { ReportId = r.ReportId, ReportName = r.ReportName }).ToList();
                }
                else
                {

                            reportTypes = ReferenceDataService.GetReportTypes(false).Select(r => new Report { ReportId = r.ReportId, ReportName = r.ReportName }).ToList();
                }


            }

            return Json(reportTypes, JsonRequestBehavior.AllowGet); ;

        }