拋出異常：System.Private.CoreLib.ni.dll中的'Microsoft.EntityFrameworkCore.DbUpdateConcurrencyException'

Question

我創建了這個包分配方法：

 [HttpPut("api/auth/user/{id}")]
    public async Task<IActionResult> AssignPackage(string id ,[FromBody] AppUser user)
    {
        try
        {
            var newUser = Mapper.Map<AppUser, UserViewModel>(user);

            var userToEdit = await _context.AppUser
            .AsNoTracking()
            .SingleOrDefaultAsync(m => m.Id == id);

            newUser.PackageType = user.AccountType;

            if (userToEdit == null)
            {
                return NotFound("Could not update user as it was not found");
            }
            else
            {
                _context.Update(user);
                await _context.SaveChangesAsync();
                //return Ok(newUser);
            }


            UserViewModel _userVM =

              Mapper.Map<AppUser, UserViewModel>(user);

            return new OkObjectResult(_userVM);
        }
        catch (DbUpdateException)
        {
            //Log the error (uncomment ex variable name and write a log.)
            ModelState.AddModelError("", "Unable to save changes. " +
                "Try again, and if the problem persists, " +
                "see your system administrator.");
            return NotFound("User not Found");
        }


    }

該方法的目的是我在郵遞員中輸入Account類型，輸出應為具有更新Package類型的用戶視圖模型。 但是，將accountType輸入postman ，輸出為'User not found'和錯誤為'404 Not found' 。

在Visual Studio中，顯示的錯誤是問題的標題。 不確定可能是什么問題（僅限初學者水平的經驗）。

使用的模型：

 public class AppUser : IdentityUser 
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string AccountType { get; set; }
        public int? PeriodOrderQty { get; set; }
        public int? TotalOrderQty { get; set; }
        public Guid? APIKey { get; set; }
        public Packages Package { get; set; }
        public Cities City { get; set; }
        public QualificationLevels Qualifications { get; set; }
        public string Token { get; set; }

    }

public class UserViewModel
    {
        public string Id { get; set; }
        public string UserName { get; set; }
        public string Email { get; set; }
        public string PackageType { get; set; }
        public int? PeriodOrderQty { get; set; }
        public int? TotalOrderQty { get; set; }
        public Guid? APIKey { get; set; }
    }

Answer 1

鑒於AppUser從IdentityUser繼承，似乎當您調用_context.Update(user); 沒有Id 。

我懷疑如果您檢查該字段，該字段將為0，因為它將作為正文的一部分出現。

因此，EF找不到要更新的實體，所以這就是您遇到異常的原因