Question

我确实尝试了一切但却无法找到灵魂在ajax上回调响应总是转到ajax的error属性而没有成功

jquery-1.9.1.min.js：5 POST http://localhost:60854/ExamController/AjaxMethodForDepartment 500（内部服务器错误）

Html代码：

   <!DOCTYPE html>
<link href="~/Content/css/bootstrap.min.css" rel="stylesheet" />
<link href="~/Content/css/bootstrap-multiselect.css" rel="stylesheet" />
<script src="~/Scripts/jquery-1.9.1.min.js"></script>
<script src="~/Scripts/bootstrap.min.js"></script>
<script src="~/Scripts/bootstrap-multiselect.js"></script>

<html>
<head>

    <title>CreateExam</title>
</head>
<body>

    <h2>Department</h2>
    <select id="dep" multiple="multiple">

    </select>

    <h2>Batch</h2>
    <select id="batch" multiple="multiple">
        <option disabled selected>-No Department Selected-</option>
    </select>

    <form action="/ExamController/CreateExam" method="post">
        <h2>Subject</h2>
        <select id="subject" multiple="multiple" name="subjects">
            <option disabled selected>-No Batch Selected-</option>
        </select><br><br>
        <input type="submit" />
    </form>
</body>
</html>



$(function () {
$("select").multiselect({
    includeSelectAllOption: true
});


$(document).ready(function () {
    $.ajax({

        type: "POST",
        url: "/ExamController/AjaxMethodForDepartment",
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function (response) {
            len = response.length;
            if (len == 0) {
                $("#dep").html('<option disabled selected>-There are no Departments in DB-</option>');
                $("#batch").html('<option disabled selected>-No Department Selected-</option>');
                $("#dep,#batch").multiselect('rebuild');
            }
            else {
                for (var i = 0; i < len; i++) {
                    if (i == 0)
                        $("#dep").html(new Option(response[i].Department_Id, response[i].Department_Id));
                    else
                        $("#dep").append(new Option(response[i].Department_Id, response[i].Department_Id));
                }
                $("#dep").multiselect('rebuild');
            }
        },
        error: function (jqXHR, textStatus, errorThrown) {
            alert("error: " + errorThrown);
            $("#dep").html('<option disabled selected>-There are no record of Departments in DB-</option>');
            $("#batch").html('<option disabled selected>-No Department Selected-</option>');
            $("#dep,#batch").multiselect('rebuild');
        }
    });
});

$("#dep").change(function () {
    var len;
    $.ajax({

        type: "POST",
        url: "/ExamController/AjaxMethodForBatch",
        data: JSON.stringify({ departments: $("#dep").val() }),
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function (response) {
            len = response.length;
            if (len == 0) {
                $("#batch").html('<option disabled selected>-Selected Department does not have any Batch-</option>');
                $("#subject").html('<option disabled selected>-No Batch Selected-</option>');
                $("#batch,#subject").multiselect('rebuild');
            }
            else {
                for (var i = 0; i < len; i++) {
                    if (i == 0)
                        $("#batch").html(new Option(response[i].Batch_Id, response[i].Batch_Id));
                    else
                        $("#batch").append(new Option(response[i].Batch_Id, response[i].Batch_Id));
                }
                $("#batch").multiselect('rebuild');
            }
        },
        error: function (response) {
            alert("Batch Error!");
            $("#batch").html('<option disabled selected>-No Department Selected-</option>');
            $("#subject").html('<option disabled selected>-No Batch Selected-</option>');
            $("#batch,#subject").multiselect('rebuild');                }
    });
});

$("#batch").change(function () {
    var len;
    $.ajax({

        type: "POST",
        url: "/ExamController/AjaxMethodForSubject",
        data: JSON.stringify({ batches: $("#batch").val() }),
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function (response) {
            len = response.length;
            if (len == 0) {
                $("#subject").html('<option disabled selected>-Selected Batch does not have any Subjects-</option>');
                $("#subject").multiselect('rebuild');
            }
            else {
                for (var i = 0; i < len; i++) {
                    if (i == 0)
                        $("#subject").html(new Option("Subject Id: " + response[i].Subject_Id + ", Subject Name: " + response[i].Subject_Name , response[i].Subject_Id));
                    else
                        $("#subject").append(new Option("Subject Id: " +response[i].Subject_Id + ", Subject Name: " + response[i].Subject_Name , response[i].Subject_Id));
                }
                $("#subject").multiselect('rebuild');
            }
        },
        error: function (response) {
            alert("Subject Error!");
            $("#subject").html('<option disabled selected>-No Batch Selected-</option>');
            $("#subject").multiselect('rebuild');
        }
    });
});

});

控制器：

    public class ExamControllerController : Controller
{
    //
    // GET: /ExamController/

    FYP_DB_Entities obj = new FYP_DB_Entities();

    public ActionResult Index()
    {
        return View();
    }


    public ActionResult CreateExam()
    {
        return View(obj.Departments.ToList());
    }

    [HttpPost]
    public ActionResult ExamCreated(int[] subjects)
    {
        Subject s = new Subject();
        Exam e = new Exam();
        Batch b = new Batch();
        foreach (var i in subjects)
        {
            s = obj.Subjects.First(x => x.Subject_Id == i);
            b = obj.Batches.First(x => x.Batch_Id == s.Batch_Id);

            e.Subject_Id = s.Subject_Id;
            e.Batch_Id = s.Batch_Id;
            e.Department_Id = b.Department_Id;
            e.Total_Marks = 50;
            e.Exam_Session = "Fall-2017";
            e.Status = "Inactive";

            obj.Exams.Add(e);
            obj.SaveChanges();
        }
        return View();
    }

    [HttpPost]
    public JsonResult AjaxMethodForDepartment()
    {
        IEnumerable<Department> departmentList = Enumerable.Empty<Department>();
        try
        {
            departmentList = obj.Departments.ToList();
            return Json(departmentList);
        }
        catch
        {
            return Json(null);
        }
    }

    [HttpPost]
    public JsonResult AjaxMethodForBatch(string[] departments)
    {
        IEnumerable<Batch> batchList = Enumerable.Empty<Batch>();
        try
        {
            batchList = departments.SelectMany(d => obj.Batches.Where(x => x.Department_Id == d));
            return Json(batchList);
        }
        catch
        {
            return Json(null);
        }
    }

    [HttpPost]
    public JsonResult AjaxMethodForSubject(string[] batches)
    {
        IEnumerable<Subject> subjectList = Enumerable.Empty<Subject>();
        try
        {
            subjectList = batches.SelectMany(d => obj.Subjects.Where(x => x.Batch_Id == d));
            return Json(subjectList);
        }
        catch
        {
            return Json(null);
        }
    }

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如何修复asp.net mvc中ajax回调的内部服务器错误500

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