你应该删除db.Books.Attach(book);

你可以使用AddOrUpdate方法:

db.Books.AddOrUpdate(book); //requires using System.Data.Entity.Migrations;
db.SaveChanges();

这里是这个问题的最佳解决方案:在视图中添加所有的ID(键)。考虑将多个表命名为(First, Second和Third)

@Html.HiddenFor(model=>model.FirstID)
@Html.HiddenFor(model=>model.SecondID)
@Html.HiddenFor(model=>model.Second.SecondID)
@Html.HiddenFor(model=>model.Second.ThirdID)
@Html.HiddenFor(model=>model.Second.Third.ThirdID)

在c#代码中，

[HttpPost]
public ActionResult Edit(First first)
{
  if (ModelState.Isvalid)
  {
    if (first.FirstID > 0)
    {
      datacontext.Entry(first).State = EntityState.Modified;
      datacontext.Entry(first.Second).State = EntityState.Modified;
      datacontext.Entry(first.Second.Third).State = EntityState.Modified;
    }
    else
    {
      datacontext.First.Add(first);
    }
    datacontext.SaveChanges();
    Return RedirectToAction("Index");
  }

 return View(first);
}

您正在尝试更新记录(对我来说这意味着“更改现有记录上的值并将其保存回来”)。因此，您需要检索对象，进行更改并保存它。

using (var db = new MyContextDB())
{
    var result = db.Books.SingleOrDefault(b => b.BookNumber == bookNumber);
    if (result != null)
    {
        result.SomeValue = "Some new value";
        db.SaveChanges();
    }
}

最简单的方法是这样的。

var book = new Model.Book
{
    BookNumber =  _book.BookNumber,
    BookName = _book.BookName,
    BookTitle = _book.BookTitle,
};
using (var db = new MyContextDB())
{
    var result = db.Books.SingleOrDefault(b => b.BookNumber == bookNumber);
    if (result != null)
    {
        try
        {
            // you can't attach book since it doesn't exist in the database yet
            // attach result instead
            db.Books.Attach(result);
            result = book; // this will update all the fields at once
            db.SaveChanges();
        }
        catch (Exception ex)
        {
            throw;
        }
    }
}

如Renat所说，删除:db.Books.Attach(book);

另外，将结果查询改为使用“AsNoTracking”，因为该查询会抛出实体框架的模型状态。它认为“结果”是现在要追踪的书，而你不想要那个。

var result = db.Books.AsNoTracking().SingleOrDefault(b => b.BookNumber == bookNumber);