当尝试使用Attach()和SaveChanges()组合更新记录时，我也有同样的问题，但我使用的是SQLite DB及其EF提供者(相同的代码在SQLServer DB中工作没有问题)。

I found out, when your DB column has GUID (or UniqueIdentity) in SQLite and your model is nvarchar, SQLIte EF treats it as Binary(i.e., byte[]) by default. So when SQLite EF provider tries to convert GUID into the model (string in my case) it will fail as it will convert to byte[]. The fix is to tell the SQLite EF to treat GUID as TEXT (and therefore conversion is into strings, not byte[]) by defining "BinaryGUID=false;" in the connectionstring (or metadata, if you're using database first) like so:

  <connectionStrings>
    <add name="Entities" connectionString="metadata=res://savetyping...=System.Data.SQLite.EF6;provider connection string=&quot;data source=C:\...\db.sqlite3;Version=3;BinaryGUID=false;App=EntityFramework&quot;" providerName="System.Data.EntityClient" />
  </connectionStrings>

链接到对我有效的解决方案: SQLite实体框架6提供者如何处理指南?

你应该删除db.Books.Attach(book);

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();
    }
}

附加实体会将其跟踪状态设置为Unchanged。要更新现有实体，您所需要做的就是将跟踪状态设置为Modified。根据EF6文档:

如果您知道数据库中已经存在一个实体，但可能已经对其进行了更改，那么您可以告诉上下文附加该实体，并将其状态设置为Modified。例如: var existingBlog =新Blog {BlogId = 1, Name = "ADO. log "。NET Blog"}; 使用(var context = new BloggingContext()) ｛ context.Entry (existingBlog)。State = EntityState.Modified; //多做点工作… context.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);
}

对于。net core

context.Customer.Add(customer);
context.Entry(customer).State = Microsoft.EntityFrameworkCore.EntityState.Modified;
context.SaveChanges();