C# 添加服务器端验证在获取用户列表时导致异常

Asp.net核心3.1

我已经扩展了IdentityUser并创建了ApplicationUser

public class ApplicationUser : IdentityUser
{
    [MaxLength ( 150 ) ] 
    public string FirstName { get ; set ; }
    [ MaxLength ( 150 ) ] 
    public string LastName { get ; set ; }
    public int AlternateUserId { get ; set ; }
    [ MaxLength ( 150 ) ] 
    public string CompanyName { get ; set ; }

    [ MaxLength ( 38 ) ] 
    [ Required ] 
    public string ClientId { get ; set ; }
    [ Required ] 
    public int ShortClient { set ; get ; }
    public bool  Locked { set ; get ; }
    public bool Admin { set ; get ; }
}

我创建了一个迁移，更新了创建所有用户的数据库。。。。。。桌子

然后，我构建了数据库以获得crud控制器和视图

这给了我这部分课程

public partial class Aspnetusers
{
   public Aspnetusers()
   {
       Aspnetuserclaims = new HashSet<Aspnetuserclaims>();
       Aspnetuserlogins = new HashSet<Aspnetuserlogins>();
       Aspnetuserroles = new HashSet<Aspnetuserroles>();
       Aspnetusertokens = new HashSet<Aspnetusertokens>();
       Usertoroles = new HashSet<Usertoroles>();
   }
   [Key]
   public string Id { get; set; }
   public string UserName { get; set; }
   public string NormalizedUserName { get; set; }
   [Required(ErrorMessage = "Please enter an email.")]
   [EmailAddress(ErrorMessage = "Please enter a valid email address.")]
   public string Email { get; set; }
   public string NormalizedEmail { get; set; }
   public bool EmailConfirmed { get; set; }
   public string PasswordHash { get; set; }
   public string SecurityStamp { get; set; }
   public string ConcurrencyStamp { get; set; }
   //  [Required(ErrorMessage = "Please enter an email.")]
   public string PhoneNumber { get; set; }
   public bool PhoneNumberConfirmed { get; set; }
   public bool TwoFactorEnabled { get; set; }
   public DateTime? LockoutEnd { get; set; }
   public bool LockoutEnabled { get; set; }
   public int AccessFailedCount { get; set; }
   //  [Required(ErrorMessage = "Please enter the first name.")]
   public string FirstName { get; set; }
   //  [Required(ErrorMessage = "Please enter the last name.")]
   public string LastName { get; set; }
   public int AlternateUserId { get; set; }
   public string CompanyName { get; set; }
   //   [Required(ErrorMessage = "You must choose a company")]
   public string ClientId { get; set; }
   public int ShortClient { get; set; }
   public bool Locked { get; set; }
   public bool Admin { set; get; }

   public virtual Company ShortClientNavigation { get; set; }
   public virtual ICollection<Aspnetuserclaims> Aspnetuserclaims { get; set; }
   public virtual ICollection<Aspnetuserlogins> Aspnetuserlogins { get; set; }
   public virtual ICollection<Aspnetuserroles> Aspnetuserroles { get; set; }
   public virtual ICollection<Aspnetusertokens> Aspnetusertokens { get; set; }
   public virtual ICollection<Usertoroles> Usertoroles { get; set; }
}

如果我调试到MS代码中，我发现了异常

“（（System.Linq.IQueryable）集合）.ElementType”引发了异常 类型为“System.NotImplementedException”

记录器返回异常

System.InvalidCastException:无法强制转换类型为的对象 “System.DBNull”以键入“System.String”。在 中的MySqlConnector.Core.Row.GetString（Int32序号） C:\projects\mysqlconnector\src\mysqlconnector\Core\Row.cs:第344行
在中的MySql.Data.MySqlClient.MySqlDataReader.GetString（Int32序号）处 C:\projects\mysqlconnector\src\mysqlconnector\MySql.Data.MySqlClient\MySqlDataReader.cs:line 272在lambda_方法（闭包、QueryContext、DbDataReader、， ResultContext，Int32[]，ResultCoordinator）位于 Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable

1.Enumerator.MoveNext（）
位于System.Collections.Generic.List

1..ctor（IEnumerable

1 collection）

在System.Linq.Enumerable.ToList[TSource]（IEnumerable

1 source）处 SextantCoreHostApp.Areas.Users.Controllers.UsersController.UserIndex（） 在里面 C:\Users\Colin\Documents\Development\SextantCore3WithPermissions\sextantcorhostapp\Areas\Users\Controllers\userscocontroller.cs:line 35分 Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfActionResultExecutor.Execute（IActionResultTypeMapper 映射器，ObjectMethodExecutor，对象控制器，对象[] （a）在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.g|u waiting | 12_0（ControllerActionInvoker 调用程序，ValueTask`1 actionResultValueTask）位于 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.g|u waiting|10_0（ControllerActionInvoker 调用程序、任务lastTask、状态next、作用域、对象状态、布尔值 完成）在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow（ActionExecutedContextSealed （上下文）在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next（状态）& 接下来，在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync（） ---来自引发异常的上一个位置的堆栈结束跟踪---在 Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g|u waiting | 24_0（ResourceInvoker 调用程序、任务lastTask、状态next、作用域、对象状态、布尔值 完成）在 Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow（ResourceExecutedContextSealed （上下文）在 Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next（状态& 接下来，在 Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync（） ---来自引发异常的上一个位置的堆栈结束跟踪---在 Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g|u Logged|17|u 1（ResourceInvoker 调用程序）在 Microsoft.AspNetCore.Builder.RouterMiddleware.Invoke（HttpContext httpContext）在 Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.g|u等待| 6|0（ExceptionHandlerMiddleware 中间件、HttpContext上下文、任务）位于 Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.HandleException（HttpContext 上下文，例外DispatchInfo edi）位于 Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.g|u等待| 6|0（ExceptionHandlerMiddleware 中间件、HttpContext上下文、任务）位于 Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke（HttpContext （上下文）在 Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke（HttpContext （上下文）在 Microsoft.AspNetCore.Localization.RequestLocalizationMiddleware.Invoke（HttpContext （上下文）在 Serilog.AspNetCore.RequestLoggingMiddleware.Invoke（HttpContext httpContext）在 Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.g|u等待| 6|0（ExceptionHandlerMiddleware 中间件、HttpContext上下文、任务

---

这里缺少什么？

用户表中的一个字段返回空值（System.DBNull），因此无法将其分配给强制字符串属性

标记为必需的字段不为空。表中只有一行数据。我再次检查，该行中的一个字段为空。这就解决了问题。谢谢

public class UsersController : Controller
{
    private readonly PCSLoginContext context;
    private ILogger<CompaniesController> logger;

    public UsersController(PCSLoginContext context,  ILogger<CompaniesController> logger)
    {
        this.context = context;
        this.logger = logger ;
    }   
    // GET: Aspnetusers
    public async Task<IActionResult> UserIndex()
    {
       var users = _context.Aspnetusers.ToList ( ) ; 
       return View( users);
    }
}

var users = _context.Aspnetusers.ToList ( ) ;