Question

尝试使用jsonresult和ajax创建级联dropdownmenu，但我不知道为什么我得到500内部服务器错误。错误发生在以下方法之上：

    [HttpGet]
    public JsonResult GetModels(string brandID="")
    {
        List<Model> models = new List<Model>();
        int ID = 0;
        if (int.TryParse(brandID, out ID))
        {
            using (CarsEntities1 dc = new CarsEntities1())
            {
         models = dc.Models.Where(a => a.Brand_ID == ID).OrderBy(a =>a.Model_name).ToList();  
            }
        }
        if (Request.IsAjaxRequest())
        {

            return new JsonResult
            {
                Data = models,
                JsonRequestBehavior = JsonRequestBehavior.AllowGet
            };
        }
        else
        {
            return new JsonResult
            {
                Data = "Not valid request",
                JsonRequestBehavior = JsonRequestBehavior.AllowGet
            };
        }
    }

我使用该方法将项目列表传递给DropDownMenu并尝试通过以下代码输出列表：

$(document).ready(function () {
        //if (typeof ($) == 'function') alert('jQuery is loaded.');
        $("#brand_Brand_ID").change(function () {
            // this will call when Brand Dropdown select change
            var brandID = parseInt($("#brand_Brand_ID").val());
            if (!isNaN(brandID)) {
                var ddModel = $("#Model_ID");
                ddModel.empty(); // this line is for clear all items from Model dropdown
                ddModel.append($("<option></option").val("").html("Select model"));
                // Here I will call Controller Action via Jquery to load Model for selected Brand
                $.ajax({
                    url: "@Url.Action("GetModels","ModelSpec")",
                    type: "GET",
                    data: { brandID: brandID },
                    dataType: "json",
                    success: function (data) {
                        if (data != null && data.success) {
                            $.each(data, function (i, val) {
                                ddModel.append(
                                        $("<option></option>").val(val.Model_ID).html(val.Model_name)
                                    );
                            });
                        }
                    },
                    error: function () {
                        alert("Fail");

                    }
                });
            }
        });
    });

我得到的是以下内容：获取http://localhost:2508/ModelSpec/GetModels?brandID=2 500内部服务器错误jquery-1.7.1.js（第8102行）

此外，我注意到当没有数据通过GetModels方法时，错误不会发生。有时我得到： GET / ModelSpec / GetModels？brandID = 5 401 Unauthorized

只要GetModels返回任何内容，就会发生错误。

The ObjectContext instance has been disposed and can no longer be used for operations that require a connection

Stacktrace： http://pastebin.com/3aXg7YiM

Answer 1

您需要在using块中移动return语句 Db上下文在您执行return语句之前处理

public JsonResult GetModels(int brandID)
{
    List<Model> models = new List<Model>();

    using (CarsEntities1 dc = new CarsEntities1())
    {
       models = dc.Models.Where(a => a.Brand_ID == brandID).OrderBy(a =>a.Model_name);
       if (Request.IsAjaxRequest())
       {
           return new JsonResult
           {
                Data = models.ToList(),
                JsonRequestBehavior = JsonRequestBehavior.AllowGet
           };
        }  
    }

    return new JsonResult
    {
        Data = "Not valid request",
        JsonRequestBehavior = JsonRequestBehavior.AllowGet
    };    
}

Answer 2

json返回类型必须是原始的，所以我相应地更改了代码（将List交换为String []并将OrderBy更改为Select：

public JsonResult GetModels(int brandID)
{
 String[] models;

using (CarsEntities1 dc = new CarsEntities1())
{
   models = dc.Models.Where(a => a.Brand_ID == brandID).Select(a=> a.Model_name).toArray();
   if (Request.IsAjaxRequest())
   {
       return new JsonResult
       {
            Data = models,
            JsonRequestBehavior = JsonRequestBehavior.AllowGet
       };
    }  
}

return new JsonResult
{
    Data = "Not valid request",
    JsonRequestBehavior = JsonRequestBehavior.AllowGet
};    
}

500内部服务器错误JsonResult mvc asp.net

2 个答案: