.net - 异常 :The object cannot be attached because it is already in the object context

Question

我正在尝试使用 Entity Framework 在循环中更新记录，如下所示:

var data = userDetails.users.Where(x => x.IsAnonymous == true);

foreach(var item in data)  
{
    var updatedData = db.Users.FirstOrDefault(x => x.UserId == item.UserId);
    updatedData.IsAnonymous = true;
    db.Users.Attach(updatedData);
    db.ObjectStateManager.ChangeObjectState(updatedData, EntityState.Modified);
    db.SaveChanges();     
}

虽然附加( db.Users.Attach(updatedData); )我有异常(exception)

The object cannot be attached because it is already in the object context. An object can only be reattached when it is in an unchanged state

我该如何解决这个错误？

Answer 1

如果这一切都发生在单个 DbContext 的上下文中(或 ObjectContext) - 只需选择记录，更新您想要的字段，然后继续。更新所有记录后 - 然后 调用 .SaveChanges()一次。不需要 Attach或 ChangeObjectState打电话……

var data = userDetails.users.Where(x => x.IsAnonymous == true);

foreach(var item in data)  
{
    var updatedData = db.Users.FirstOrDefault(x => x.UserId == item.UserId);

    if(updatedData != null)
    {
        updatedData.IsAnonymous = true;
    }
}

db.SaveChanges();     

由于您刚刚选择了 updatedData来自 db.Users数据集 - 它已经是对象集的一部分 - 无需再次附加它!只需更新您需要的内容，然后调用 .SaveChanges() (最好是整批一次——而不是每条记录一次......)