Question

我不知道为什么我得到的序列中没有元素我有点新mvc

我的控制器

 [HttpPost]
            public ActionResult DeleteAnnounce(string announce)
            {
                using (var db = new HarmonyMainServerDbContext())
                {
                    ANNOUNCEMENT annoude = db.Announcer.First(c => c.AnnounceTitle == announce);
                    db.Announcer.Remove(annoude);
                    db.SaveChanges();
                }
                return RedirectToAction("ViewAnnounce");
            }

我的观点

<div id="clientDetailsContainer">
    @using (Html.BeginForm("Announcements", "Admin", FormMethod.Post, new { id = "Announcers" }))
    {
        @Html.AntiForgeryToken()
        @Html.ValidationSummary(true)

            <div class="module-controls" style="display:block;">
               <a href="/Admin/ViewAnnounce" class="k-button module-action"><img src="../Images/src/back.png"/><span>Back to List</span></a>
               <a class="k-button module-action" id="submitSave" title="haha"><img src="../Images/src/subgrid_save.png"/><span>Save</span></a>
               <a class="k-button module-action" id="submitDelete" ><img src="../Images/src/subgrid_save.png"/><span>Delete</span></a>
            </div>

        <h2>Announcement</h2>
        @Html.HiddenFor(model => model.AnnounceID)
        <div class="client-details" style="margin-left: 50px">




             <p>
                <label class="label-ant">Announcement Title</label>
                @Html.TextBoxFor(model => model.AnnounceTitle, new {@class="k-textbox", @style="width:250px" })
                @Html.ValidationMessageFor(model => model.AnnounceTitle)
            </p>

            <p>
                <label class="label-ant">Announcement Remarks</label>
                @Html.TextBoxFor(model => model.AnnounceRemarks, new {@class="k-textbox", @style="width:250px" })
                @Html.ValidationMessageFor(model => model.AnnounceRemarks)
            </p>

            <p>
                <label class="label-ant">Announce Link</label>
                @Html.TextBoxFor(model => model.AnnounceLink, new {@class="k-textbox", @style="width:250px" })
                @Html.ValidationMessageFor(model => model.AnnounceLink)
            </p>

        </div>
    }
   <script>
       $("#submitSave").click(function () {
           $("#Announcers").submit();
       });
       $("#submitDelete").click(function () {
           $("#Announcers").attr({
               "action" : "/Admin/DeleteAnnounce",
           });
       });
   </script>

</div>

Answer 1

在收集中，您需要了解差异的方法很少

首先 - 表示如果没有返回任何内容，它将抛出异常，但它允许收集不仅仅是第一次
单一 - 表示只获得一个项目，因此如果集合匹配超过一个或者你将得到例外，这是善意的“约束”
FirstOrDefault - 表示集合可以包含多个或不匹配的项目
SingleOrDefault - 集合应该只有一个或非项目匹配项

Answer 2

这是因为你正在使用First（）。如果没有具有匹配标题的播音员，则抛出异常。

请参阅https://msdn.microsoft.com/library/bb291976%28v=vs.100%29.aspx

序列在mvc上不包含任何元素

2 个答案: