抛出异常：System.Private.CoreLib.ni.dll中的'Microsoft.EntityFrameworkCore.DbUpdateConcurrencyException'

Question

我创建了这个包分配方法：

 [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");
        }


    }

该方法的目的是我在邮递员中输入Account类型，输出应为具有更新Package类型的用户视图模型。 但是，将accountType输入postman ，输出为'User not found'和错误为'404 Not found' 。

在Visual Studio中，显示的错误是问题的标题。 不确定可能是什么问题（仅限初学者水平的经验）。

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

鉴于AppUser从IdentityUser继承，似乎当您调用_context.Update(user); 没有Id 。

我怀疑如果您检查该字段，该字段将为0，因为它将作为正文的一部分出现。

因此，EF找不到要更新的实体，所以这就是您遇到异常的原因