MVC3 AJAX级联DropDownLists(MVC3 AJAX Cascading DropD

我有一个很难搞清楚如何让级联下拉列表，为我的asp.net MVC3应用工作。我有一个弹出框，我想显示2个dropdownlists的基础上，什么是第一选择第二个被填充。每次我运行应用程序的控制方法返回值的正确列表，但不是打Ajax调用的成功部分我打的错误部分。我已经做了很多的研究和随后的几个例子，我发现，但事情仍然不完全正确，任何帮助将不胜感激。

编辑：使用萤火进一步检查示出一条错误500内部服务器错误：异常详细信息：System.InvalidOperationException：检测到循环引用而序列化类型的对象“System.Data.Entity.DynamicProxies.GameEdition

我有以下的jQuery / AJAX：

<script type="text/javascript">
$(function () {
    $("#PlatformDropDownList").change(function () {
        var gameId = '@Model.GameID';
        var platformId = $(this).val();
        // and send it as AJAX request to the newly created action 
        $.ajax({
            url: '@Url.Action("Editions")',
            type: 'GET',
            data: { gameId: gameId, platformId: platformId },
            cache: 'false',
            success: function (result) {
                $('#EditionDropDownList').empty();
                // when the AJAX succeeds refresh the ddl container with 
                // the partial HTML returned by the PopulatePurchaseGameLists controller action 
                $.each(result, function (result) {
                    $('#EditionDropDownList').append(
                        $('<option/>')
                            .attr('value', this.EditionID)
                            .text(this.EditionName)
                    );

                });
            },
            error: function (result) {
                alert('An Error has occurred');
            }
        });
    });
});

这里是我的控制器方法：

  public JsonResult Editions(Guid platformId, Guid gameId)
  {
     //IEnumerable<GameEdition> editions = GameQuery.GetGameEditionsByGameAndGamePlatform(gameId, platformId);
     var editions = ugdb.Games.Find(gameId).GameEditions.Where(e => e.PlatformID == platformId).ToArray<GameEdition>();

     return Json(editions, JsonRequestBehavior.AllowGet);
  }

这里是我的网页的HTML表单：

<div id="PurchaseGame">
@using (Html.BeginForm())
{
    @Html.ValidationSummary(true, "Please correct the errors and try again.")
    <div>
        <fieldset>
            <legend></legend>
            <p>Select the platform you would like to purchase the game for and the version of the game you would like to purchase.</p>

            <div class="editor-label">
                @Html.LabelFor(model => model.PlatformID, "Game Platform")
            </div>
            <div class="editor-field">
                @Html.DropDownListFor(model => model.PlatformID, new SelectList(Model.Platforms, "GamePlatformID", "GamePlatformName"), new { id = "PlatformDropDownList", name="PlatformDropDownList" })
            </div>

            <div class="editor-label">
                @Html.LabelFor(model => model.EditionID, "Game Edition")
            </div>
            <div id="EditionDropDownListContainer">
                @Html.DropDownListFor(model => model.EditionID, new SelectList(Model.Editions, "EditionID", "EditionName"), new { id = "EditionDropDownList", name = "EditionDropDownList" })
            </div>

            @Html.HiddenFor(model => model.GameID)
            @Html.HiddenFor(model => model.Platforms)

            <p>
                <input type="submit" name="submitButton" value="Purchase Game" />
                <input type="submit" name="submitButton" value="Cancel" />
            </p>

        </fieldset>
    </div>
}

您不能发送使用GET动词JSON编码的请求。所以更换type: 'GET'与type: 'POST' ，它会工作。另外，由于已指定JSON请求你必须，以及，发送其与实现JSON请求JSON.stringify功能： data: JSON.stringify({ gameId: gameId, platformId: platformId }), 但是，因为你只有两个值我觉得用GET会更容易些。所以我的建议是去除contentType: 'application/json'参数，让你的AJAX请求是这样的：

$.ajax({
    url: '@Url.Action("Editions")',
    type: 'GET',
    data: { gameId: gameId, platformId: platformId },
    cache: 'false',
    success: function (result) {
        $('#EditionDropDownList').empty();
        // when the AJAX succeeds refresh the ddl container with 
        // the partial HTML returned by the PopulatePurchaseGameLists controller action 
        if(result.length > 0)
        {
            $.each(result, function (result) {
                $('#EditionDropDownList').append(
                    $('<option/>')
                         .attr('value', this.EditionID)
                         .text(this.EditionName)
                );
            });
        }
        else
        {
            $('#EditionDropDownList').append(
                $('<option/>')
                    .attr('value', "")
                    .text("No edition found for this game")
            );
        }

    },
    error: function () {
        alert('An Error has occured');
    }
});

另外在DropDownListFor在剃刀标记辅助我注意到以下几点：

onchange = "Model.PlatformID = this.value;"

我可以说的是，这并没有做什么，你可能会认为它。

更新：

看来你是因为你是通过你得到一个圆形对象引用错误editions的领域模型JSON的方法。循环引用的对象层次不能被JSON序列。再说你不需要通过发送包含在此版本的客户端的所有废话浪费带宽。所有客户需要的是编号和名称的集合。因此，简单地使用视图模型：

public ActionResult Editions(Guid platformId, Guid gameId)
{
    var editions = ugdb
        .Games
        .Find(gameId)
        .GameEditions
        .Where(e => e.PlatformID == platformId)
        .ToArray<GameEdition>()
        .Select(x => new 
        {
            EditionID = x.EditionID,
            EditionName = x.EditionName
        })
        .ToArray();

    return Json(editions, JsonRequestBehavior.AllowGet);
}