C# SaveChanges返回0，并且根本不保存数据

实体框架的

SaveChanges（）

方法遇到了一个奇怪的问题。问题是它返回0，并且根本不更新表数据。问题可能是什么？有什么想法吗？我必须更新现有的用户数据

[HttpPost]
[Authorize(Roles = "User")]
public ActionResult Settings(User _users)
{
    using (MydbEntities db = new MydbEntities())
    {
        var u = new User();
        string _Email = User.Identity.GetUserId().ToString();

        if(db.Users.Any(x=>x.Email == _Email))
        {
            u.BusinessName = _users.BusinessName;
            u.Address = _users.Address;
            u.VatNumber = _users.VatNumber;
            u.PhoneNumber = _users.PhoneNumber;
            u.IsBusinessUser = _users.IsBusinessUser;

            var foo = db.SaveChanges();
        }
    }
}

我相信您正在尝试的是加载现有用户，如果它存在，则更新它

请尝试以下代码：

[HttpPost]
[Authorize(Roles = "User")]
public ActionResult Settings(User _users)
{
    using (MydbEntities db = new MydbEntities())
    {
        string _Email = User.Identity.GetUserId().ToString();

        // try to find the existing user in the database
        User existing = db.Users.FirstOrDefault(x => x.Email == _Email);

        if(existing != null)
        {
            // if you *DID* find a user - then update its properties
            existing.BusinessName = _users.BusinessName;
            existing.Address = _users.Address;
            existing.VatNumber = _users.VatNumber;
            existing.PhoneNumber = _users.PhoneNumber;
            existing.IsBusinessUser = _users.IsBusinessUser;

            var foo = db.SaveChanges();
        }
    }
}

首先，您加载现有用户，如果找到了一个，则更新其属性，现在

SaveChanges（）

调用应该为您更新该现有用户