当 IDENTITY_INSERT 设置为 OFF 时，无法在表“MyTableName”中插入标识列的显式值

Question

我正在使用 ASP.Net MVC 6

我的控制器功能：

// POST: MyManyToManies/Create
[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult Create(MyManyToMany myManyToMany)
{
    if (ModelState.IsValid)
    {


        _context.TestManyToMany.Add(myManyToMany);
        _context.SaveChanges();
        //==========Get Last Inserted ID==============//
        int LastInsertedID = _context.TestManyToMany.Max(c => c.ID);
        string[] agencies = Request.Form["agencies"].ToArray();

        MyManyRelAgency Rel = new MyManyRelAgency();

        foreach (string aitem in agencies)
        {
            int d = int.Parse(aitem);
            Rel.AgencyID = d;
            Rel.MyManyID = LastInsertedID;

            _context.Add(Rel);
            _context.SaveChanges();
        }
        return RedirectToAction("Index");
    }
    return View(myManyToMany);
}

我的模型 1

public class MyManyToMany
{
    public int ID { get; set; }
    public string FirstName { get; set; }
}

用于插入相关商品 ID 的模型 2：

public class MyManyRelAgency
{
    [Key]
    public int ID { get; set; }
    public int MyManyID { get; set; }
    public int AgencyID { get; set; }
}

我的观点：

@model UNTest.Models.MyManyToMany

@{
    ViewData["Title"] = "Create";
 }

<h2>Create</h2>

<form asp-action="Create">
    <div class="form-horizontal">
       <h4>MyManyToMany</h4>
       <hr />
       <div asp-validation-summary="ValidationSummary.ModelOnly" class="text-danger"></div>
       <div class="form-group">
           <label asp-for="FirstName" class="col-md-2 control-label"></label>
            <div class="col-md-10">
                <input asp-for="FirstName" class="form-control" />
               <span asp-validation-for="FirstName" class="text-danger" />
            </div>
        </div>

        <div class="form-group">
        <label class="col-md-2 control-label">Province</label>
        <div class="col-md-10">
            @Html.DropDownList("agencies", (List<SelectListItem>)ViewBag.options, htmlAttributes: new { @class = "form-control",@multiple="multiple" })
        </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>
</form>

<div>
   <a asp-action="Index">Back to List</a>
</div>

当我点击插入时出现以下错误：

Cannot insert explicit value for identity column in table 'MyManyRelAgency' when IDENTITY_INSERT is set to OFF

Answer 1

如果你需要在 ID 上插入一个值，试试这个

[Required, Key, DatabaseGenerated(DatabaseGeneratedOption.None)]
 public int ID{ get; set; }

Answer 2

当您添加具有 ID 的实体时，您会在 EF 中收到此错误。通常这个实体已经存在于数据库中。要修改实体，请使用以下示例：

_context.TestManyToMany.Add(myManyToMany);

改成

foreach(var e in myManyToMany)
    _context.Entry(e).State = EntityState.Modified;

Answer 3

如果这是您想要做的事情，当您的 id 列是标识列时，您需要运行 SET IDENTITY_INSERT dbo.YOUR_TABLE_NAME ON; 才能使其工作。这使您可以将 ID 插入标识列。 但是，在具有标识列的表中插入新行时，您不需要指定 ID :)

或者您是否尝试更新已经存在的行？

Answer 4

研究本站后：

http://www.entityframeworktutorial.net/entityframework6/addrange-removerange.aspx

通过使用 List 和 AddRange

我解决了我的问题，请参阅下面的 Create Function 代码，它运行良好：

      // POST: MyManyToManies/Create
    [HttpPost]
    [ValidateAntiForgeryToken]
    public IActionResult Create(MyManyToMany myManyToMany)
    {
        if (ModelState.IsValid)
        {


            _context.TestManyToMany.Add(myManyToMany);

            _context.SaveChanges();
            //==========Get Last Inserted ID==============//
            int LastInsertedID = _context.TestManyToMany.Max(c => c.ID);
            string[] agencies = Request.Form["agencies"].ToArray();

            //MyManyRelAgency Rel = new MyManyRelAgency();
            IList<MyManyRelAgency> TheRel = new List<MyManyRelAgency>();
            foreach (string aitem in agencies)
            {
                int d = int.Parse(aitem);

                TheRel.Add(new MyManyRelAgency() { AgencyID = d, MyManyID = LastInsertedID });
                //Rel.AgencyID = d;
                //Rel.MyManyID = LastInsertedID;



            }
            _context.MyManyToManyRelWithAgency.AddRange(TheRel);
            _context.SaveChanges();
            return RedirectToAction("Index");
        }
        return View(myManyToMany);
    }