INSERT 语句与 FOREIGN KEY 冲突，但 debug window 显示正确的值

Question

大家好，我是 asp.net mvc 的新手，目前正在从事我的大学项目，这是一个大学门户网站，使用 entity framework 代码优先方法。但是我收到一个错误 **

The INSERT statement conflicted with the FOREIGN KEY constraint "FK_dbo.Notices_dbo.Colleges_CollegeId". The conflict occurred in database "aspnet-QuickPly5-20180306011920", table "dbo.Colleges", column 'Id'.

** 我在整个网络上搜索解决方案，每个人都建议在将数据输入到外键 table 之前，要插入的值应该存在于主 table 中。我的模型类如下

Collge.cs

public class College
{

     public int Id { get; set; }

     [Required]
     public string Name { get; set; }

     [Required]
     public string Email { get; set; }

     [Required]
     public string Phone { get; set; }

     [Required]
     public string Address { get; set; }

}

Notice.cs

public class Notice {

        public int Id { get; set; }

        [Required]
        public string Title { get; set; }

        public string Description { get; set; }

        public string ImagePath { get; set; }

        [Required]
        public DateTime DatePosted { get; set; }

        //public bool IsPublic { get; set; }

        public College College { get; set; }

        public int CollegeId { get; set; }

    }

NoticeController.cs

[HttpPost]
        public ActionResult ProcessForm(Notice notice, HttpPostedFileBase file)
        {
            if (file != null)
            {
                var fileName = Guid.NewGuid() + "-" + file.FileName;
                notice.ImagePath = Server.MapPath(Path.Combine("~/uploads/notice/" + fileName));

                file.SaveAs(notice.ImagePath);
            }

            if (notice.Id == 0)
            {
                notice.DatePosted = DateTime.Now;
                _context.Notice.Add(notice);
            }
            else
            {
                var noticeInDb = _context.Notice.Single(n => n.Id == notice.Id);

                notice.Title = noticeInDb.Title;
                notice.Description = noticeInDb.Description;
                notice.ImagePath = noticeInDb.ImagePath;
                //notice.IsPublic = noticeInDb.IsPublic;
            }

            _context.SaveChanges();

            return View("Index");
        }

Table定义

通知

CREATE TABLE [dbo].[Notices] (
    [Id]          INT            IDENTITY (1, 1) NOT NULL,
    [Title]       NVARCHAR (MAX) NOT NULL,
    [Description] NVARCHAR (MAX) NULL,
    [ImagePath]   NVARCHAR (MAX) NULL,
    [DatePosted]  DATETIME       NOT NULL,
    [CollegeId]   INT            NOT NULL,
    CONSTRAINT [PK_dbo.Notices] PRIMARY KEY CLUSTERED ([Id] ASC),
    CONSTRAINT [FK_dbo.Notices_dbo.Colleges_CollegeId] FOREIGN KEY ([CollegeId]) REFERENCES [dbo].[Colleges] ([Id]) ON DELETE CASCADE
);

GO
CREATE NONCLUSTERED INDEX [IX_CollegeId]
    ON [dbo].[Notices]([CollegeId] ASC);

大学

CREATE TABLE [dbo].[Colleges] (
    [Id]      INT            IDENTITY (1, 1) NOT NULL,
    [Name]    NVARCHAR (MAX) NOT NULL,
    [Email]   NVARCHAR (MAX) NOT NULL,
    [Phone]   NVARCHAR (MAX) NOT NULL,
    [Address] NVARCHAR (MAX) NOT NULL,
    CONSTRAINT [PK_dbo.Colleges] PRIMARY KEY CLUSTERED ([Id] ASC)
);

当我运行应用程序正常时，我从标题中得到异常，但在调试 window 中，当我检查它时显示 CollegeId = 1 ( table) 和 NoticeId = 6 中只有一行（已经很少有通知了）。我可以手动正确地将数据添加到 table 而不会出现任何错误。

我不明白我做错了什么。

提前致谢。（对不起我的英语）

Debug window screenshot

Answer 1

输入你的学院 class 并通知 class 像这样：

public class College
{
 //...

 public ICollection<Notice> Notice{ get; set; }

}

public class Notice
{
 //...

 [ForeignKey("College")]
 public int CollegeId { get; set; }
 public College College { get; set; }
}

Answer 2

我觉得你的问题从观点上看。我重写代码。它按照代码工作。

创建视图：

@model Whosebugquestion1.Models.Notice

@{
    ViewBag.Title = "Create";
}

<h2>Create</h2>


@using (Html.BeginForm("ProcessForm", "Notice", FormMethod.Post))
{
    @Html.AntiForgeryToken()

    <div class="form-horizontal">
        <h4>Notice</h4>
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })
        <div class="form-group">
            @Html.LabelFor(model => model.Title, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Title, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Title, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.Description, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Description, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Description, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.ImagePath, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.ImagePath, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.ImagePath, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.DatePosted, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.DatePosted, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.DatePosted, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.CollegeId, "CollegeId", htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.TextBox("CollegeId", null, htmlAttributes: new { @class = "form-control" })
                @Html.ValidationMessageFor(model => model.CollegeId, "", new { @class = "text-danger" })
            </div>
        </div>

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

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

我更改了代码：

[HttpPost]
        public ActionResult ProcessForm(Notice notice, HttpPostedFileBase file)
        {
            if (file != null)
            {
                var fileName = Guid.NewGuid() + "-" + file.FileName;
                notice.ImagePath = Server.MapPath(Path.Combine("~/uploads/notice/" + fileName));

                file.SaveAs(notice.ImagePath);
            }

            if (notice.Id == 0)
            {
                //notice.DatePosted = DateTime.Now;
                _context.Notice.Add(notice);
            }
            else
            {

                _context.Entry(notice).State = EntityState.Modified;

                //var noticeInDb = _context.Notice.Single(n => n.Id == notice.Id);

                //notice.Title = noticeInDb.Title;
                //notice.Description = noticeInDb.Description;
                //notice.ImagePath = noticeInDb.ImagePath;
                //notice.IsPublic = noticeInDb.IsPublic;
            }
            //_context.Notice.Add(notice);

            _context.SaveChanges();

            return View("Index", _context.Notice);
        }

和索引控制器：包括将 College 属性设置为通知模型的方法。

// GET: Notice
        public ActionResult Index()
        {
            var model = _context.Notice.Include(i => i.College);

            return View(model);
        }

INSERT 语句与 FOREIGN KEY 冲突，但 debug window 显示正确的值

The INSERT statement conflicted with the FOREIGN KEY, but debug window shows correct values

c#

asp.net-mvc

entity-framework

ef-code-first