创建方法尝试从表单中插入 FK 作为 ID

Question

我正在尝试将新数据插入到我的一个表中，但我收到了身份插入错误，即使我从未真正设置过 ID。

我可以用创可贴修复此问题，但我想了解为什么会发生这种情况以及最佳实践是什么

如果我在添加到 DbContext 之前将 Id 设置为 0，它可以正常工作，但我根本不明白我的 Id 是在哪里设置的。

这是我的模型：

public class Question : BaseModel

{

    public QuestionGroup QuestionGroup { get; set; }

    public int QuestionGroupId { get; set; }

    [Display(Name ="Question Text")]

    public string QuestionText { get; set; }

    public string Type { get; set; }}

public class BaseModel

{

    public int Id { get; set; }

    [Display(AutoGenerateField = false), JsonIgnore]

    public DateTime CreatedAt { get; set; }

    [Display(AutoGenerateField = false), JsonIgnore]

    public DateTime UpdatedAt { get; set; }

}

这是我的相关控制器代码：（如果我取消注释将 Id 设置为 0，则可以正常工作）

[HttpPost]

[ValidateAntiForgeryToken]

public async Task<IActionResult> Create(Question question)

{

    //question.Id = 0;

    if (ModelState.IsValid)

    {

        _context.Add(question);

        await _context.SaveChangesAsync();

        return RedirectToAction("Details", "QuestionGroups", new { id = 

        question.QuestionGroupId });

    }

    await PopulateId(question.QuestionGroupId);

    return View(question);

}

这是我的表格：

<div class="col-md-4">

    <form asp-action="Create" enctype="multipart/form-data">

        <div asp-validation-summary="ModelOnly" class="text-danger"></div>

        <input asp-for="QuestionGroupId" type="hidden" 

        value="@ViewBag.QuestionGroupId"/>

        <div class="form-group">

            <label asp-for="QuestionText" class="control-label"></label>

            <input asp-for="QuestionText" class="form-control" />

            <span asp-validation-for="QuestionText" class="text-danger></span>

        </div>

这是有道理的，因为当我调试时，我看到的是：

Answer 1

很奇怪。我所能建议的只是尝试使 Id 属性不是自动的，以通过查看调用堆栈来找出它的设置位置。private int _id;public int Id&nbsp;{&nbsp;&nbsp; &nbsp;get { return _id; }&nbsp; &nbsp;set { _id = value; }&nbsp;}并使用“set”设置断点

Answer 2

ASP.NET Core我尝试通过使用以下代码创建项目来重新生成您的错误：public class BaseModel{&nbsp; &nbsp; public int Id { set; get; }&nbsp; &nbsp; public DateTime CreatedAt { get; set; }&nbsp; &nbsp; public DateTime UpdatedAt { get; set; }}public class Question : BaseModel{&nbsp; &nbsp; public string QuestionText { get; set; }&nbsp; &nbsp; public string Type { get; set; }}//Startup.cs&nbsp; &nbsp; &nbsp; &nbsp; services.AddDbContext<ApplicationDbContext>(options =>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; options.UseSqlite(&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Configuration.GetConnectionString("DefaultConnection")&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; );&nbsp; &nbsp; &nbsp; &nbsp; });//Home Controller&nbsp; &nbsp; public IActionResult Test()&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; _applicationDbContext.Questions.Add(new Question&nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Id = 0, //Changing this value affects the behaviour of the application&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; QuestionText = "Question text"&nbsp; &nbsp; &nbsp; &nbsp; });&nbsp; &nbsp; &nbsp; &nbsp; _applicationDbContext.SaveChanges();&nbsp; &nbsp; &nbsp; &nbsp; return View(_applicationDbContext.Questions.ToList());&nbsp; &nbsp; }但是，我无法重新生成您的相同错误。当Id(Test()方法中) 未设置或设置为等于 0 时，它可以工作。如果我设置为大于 0 的数字，例如 100，它第一次可以工作，但在下次运行中会失败，并显示以下错误消息：SQLite 错误 19：“UNIQUE 约束失败：Questions.Id”如您所见，我在这里使用 SQLite。生成的迁移如下：&nbsp; &nbsp; &nbsp; &nbsp; protected override void Up(MigrationBuilder migrationBuilder)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; migrationBuilder.CreateTable(&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; name: "Questions",&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; columns: table => new&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Id = table.Column<int>(nullable: false)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .Annotation("Sqlite:Autoincrement", true),&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; CreatedAt = table.Column<DateTime>(nullable: false),&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; UpdatedAt = table.Column<DateTime>(nullable: false),&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; QuestionText = table.Column<string>(nullable: true),&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Type = table.Column<string>(nullable: true)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; },&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; constraints: table =>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; table.PrimaryKey("PK_Questions", x => x.Id);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; });&nbsp; &nbsp; }这里，Idfield被创建为身份字段。我可以得出的结论是，您的Id字段是作为identity数据库自动设置的字段创建的。所以你不应该为它设置一个特定的值。也许在您处理的某个地方设置了非零值。正如 @feihoa 所说，此时的断点和调试会话可能会有所帮助。startup.cs如果问题仍然存在，您的配置代码、迁移代码以及有关您正在使用的数据库类型的信息可能会有所帮助。

Answer 3

事实证明，我的问题实际上出在我的 create 方法中。这是损坏的代码：// GET: Questions/Create&nbsp; &nbsp; &nbsp; &nbsp; public IActionResult Create(int? id)&nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (id == null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return NotFound();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; PopulateId(id);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return View();&nbsp; &nbsp; &nbsp; &nbsp; }修复：// GET: Questions/Create&nbsp; &nbsp; &nbsp; &nbsp; public IActionResult Create(int? questionGroupId)&nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (questionGroupId== null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return NotFound();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; PopulateId(questionGroupId);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return View();&nbsp; &nbsp; &nbsp; &nbsp; }由于默认启动有这个模板：app.UseMvc(routes =>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; routes.MapRoute(&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; name: "default",&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; template: "{controller=Home}/{action=Index}/{id?}");&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; });综上所述：这是一个非常简单的错误，因为我使用了糟糕的命名。默认的 create get 方法没有 ID，但由于我需要对页面上的父对象执行一些操作，因此我必须将其传递到我的视图，并且 .Net 将我的 QuestionId（子级）设置为 QuestionGroupId （父）。我希望这对遇到此问题的其他人有所帮助。感谢评论者的帮助