如何延迟 ajax 响应 - asp.net mvc 使用局部视图

Question

我的下拉列表数据正在视图中使用 ajax 助手传递给控制器，在控制器中，部分视图使用这些数据返回。当我运行应用程序查看局部视图时，它抛出一个错误：

An exception of type 'System.Data.Entity.Core.EntityCommandExecutionException' occurred in EntityFramework.SqlServer.dll but was not handled in user code

但是，当我慢慢调试时，部分视图在页面中正确显示。我假设由于部分视图在调试模式下按照我的预期正确显示，我可能需要延迟 ajax 的响应？这是正确的方法吗？有什么想法吗？

查看：

@using (Ajax.BeginForm("GetEmployee", "Employee", new AjaxOptions
{
    HttpMethod = "POST",    
    UpdateTargetId = "showResult"
})) 
{
    @Html.AntiForgeryToken()

    <div class="form-horizontal">   
        <div class="form-group">
            <label class="control-label col-md-2" for="CountryId">Country</label>
            <div class="col-md-10">
                @Html.DropDownList("CountryId", null, "-- Select Country --", new { @class = "form-control", @onchange = "FillCity()" })                
            </div>
        </div>

        <div class="form-group">
            <label class="control-label col-md-2" for="City">City</label>
            <div class="col-md-10">
                @Html.DropDownListFor(m => m.City, new SelectList(Enumerable.Empty<SelectListItem>(), "CityId", "CityName"), "-- Select City --", new { @class = "form-control" })              
            </div>
        </div>       

        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Search" class="btn btn-default" />
            </div>
        </div>
    </div>
}

<div id="showResult"></div>

@section Scripts {    
    @Scripts.Render("~/bundles/jqueryval")
    <script src="~/Scripts/jquery.unobtrusive-ajax.min.js"></script>
    <script>
        function FillCity() {
            var countryId = $('#CountryId').val();
            $.ajax({
                url: '/Posting/FillCity',
                type: "GET",
                dataType: "JSON",
                data: { country: countryId },
                success: function (cities) {
                    $("#City").html(""); // clear before appending new list
                    $("#City").append($('<option>-- Select City --</option>'))
                    $.each(cities, function (i, city) {
                        $("#City").append($('<option></option>').val(city.CityId).html(city.CityName));
                    });
                }
            });
        }
    </script>
}

控制器：

[HttpPost]
public ActionResult GetEmployee(int CountryId, int city)
{
    var model = db.Employees
        .Where(x => x.Country.CountryId == CountryId && x.City.CityId == city);
    return PartialView("PartialEmployee", model);
}

局部视图：

@model IEnumerable<PokeGoTradeModel.Models.Employee>

<table class="table">
    <tr>        
        <th>Country</th>       
        <th>City</th>        
    </tr>
    @foreach (var item in Model)
    {
        <tr>         
            <td>@Html.DisplayFor(modelItem => item.Country.CountryName)</td>
            <td>@Html.DisplayFor(modelItem => item.City.CityName)</td> 
        </tr>
    }
</table>

这是我的内部异常堆栈跟踪：

   at System.Data.SqlClient.SqlInternalConnectionTds.ValidateConnectionForExecute(SqlCommand command)
   at System.Data.SqlClient.SqlConnection.ValidateConnectionForExecute(String method, SqlCommand command)
   at System.Data.SqlClient.SqlCommand.ValidateCommand(String method, Boolean async)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
   at System.Data.Common.DbCommand.ExecuteReader(CommandBehavior behavior)
   at System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.<Reader>b__c(DbCommand t, DbCommandInterceptionContext`1 c)
   at System.Data.Entity.Infrastructure.Interception.InternalDispatcher`1.Dispatch[TTarget,TInterceptionContext,TResult](TTarget target, Func`3 operation, TInterceptionContext interceptionContext, Action`3 executing, Action`3 executed)
   at System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.Reader(DbCommand command, DbCommandInterceptionContext interceptionContext)
   at System.Data.Entity.Internal.InterceptableDbCommand.ExecuteDbDataReader(CommandBehavior behavior)
   at System.Data.Common.DbCommand.ExecuteReader(CommandBehavior behavior)
   at System.Data.Entity.Core.EntityClient.Internal.EntityCommandDefinition.ExecuteStoreCommands(EntityCommand entityCommand, CommandBehavior behavior)

Answer 1

我明白了。这都是因为延迟加载。所以我的员工模型具有国家和城市的导航属性。在我的 Actionresult GetEmployee 方法中，我需要添加更多包含员工模型导航属性的行。例如，

var model = db.employees.Include(x=>x.Country)
                        .Include(x=>x.City)
                        .Where(x=>x.Country.CountryId=countryId && x.City.CityId=cityId);

希望对大家在使用ajax局部视图时遇到类似问题的朋友有所帮助。如果您在模型中使用虚拟属性，例如：

public virtual Country Country { get; set; }

确保在查询中使用 Include。

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