數據為空。 不能對 Null 值調用此方法或屬性。 實體框架核心

Question

我試圖獲取數據列表，但從GetAllList()方法獲取空值。 在這個項目中，我使用 .Net core 和 ORM Entity Framework core code first method with repository pattern

實體類

public class SIDGenerator
{
    public int Id { get; set; }
    public string TrackId { get; set; }
    public string Track { get; set; }
    public string SId { get; set; }
    public int InstanceNumber { get; set; }
    public string Comment { get; set; }
    public bool InUse { get; set; }
    public bool IsOtherSysType { get; set; }
    public bool IsDeployed { get; set; }
    public string Exception { get; set; }
   
    public DateTime ReservationDate { get; set; }
    public DateTime LastUpdated { get; set; }
    public bool IsDeleted { get; set; }
    public bool IsManuallyDefined { get; set; }
    public int ReservatedBy { get; set; }
}

界面

public interface ISidGeneratorRepository<T> where T :SIDGenerator
{
    T GetById(int id);

    /// <returns>List of the entity</returns>
    List<T> GetAllList();
}

執行

public class SidGeneratorRepository<T> : ISidGeneratorRepository<T> where T : SIDGenerator
{
    private readonly SHIELDDbContext _dbContext;
    private readonly ILoggerManager _logger;
    private readonly IDateTime _date;
    public SidGeneratorRepository(SHIELDDbContext dbContext, ILoggerManager logger, IDateTime date)
    {
        _dbContext = dbContext;
        _logger = logger;
        _date = date;
    }
 
    public void Delete(SIDGenerator entity)
    {
        throw new NotImplementedException();
    }

    public void DeleteById(int id)
    {
        throw new NotImplementedException();
    }

    public List<T> GetAllList()
    {
        var result= _dbContext.Set<T>()//This statement causes exception data is null
               .ToList();
        return result;
    }

    public T GetById(int id)
    {
        var sid = _dbContext.Set<T>()
                    .FirstOrDefault(i => i.Id == id);
        if (sid == null)
        {
            throw new NotFoundException("Sid could not be found with id " + id.ToString(), id);
        }

        return sid;
    }
}

這是我的 dbcontext 類

public class SHIELDDbContext : DbContext
{
    public SHIELDDbContext(DbContextOptions<SHIELDDbContext> options)
        : base(options)
    {
    }

    public DbSet<SIDGenerator> SIDGenerator { get; set; }
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.ApplyConfigurationsFromAssembly(typeof(UserRoleSeedConfig).Assembly);
    }
}

下面是我的處理程序類

public Task<GetAllSidViewModel> Handle(GetAllSidQuery request, CancellationToken cancellationToken)
{
    try
    {
        
        var sidList = _sidRepository.GetAllList();
        if (sidList?.Count > 0)
        {
            var viewModel = new GetAllSidViewModel
            {
                sIDlist = sidList
            };
            return Task.FromResult(viewModel);
        }

        return null;
    }
    catch (Exception ex)
    {
        _logger.LogError("Could not retrieve SID LIST from DB" + ex);
        return null;
    }
}

下面是上述實體的表腳本

CREATE TABLE [dbo].[SIDGenerator](
    [Id] [int] IDENTITY(1,1) NOT NULL,
    [Track] [nvarchar](max) NULL,
    [TrackId] [nvarchar](max) NULL,
    [SId] [nvarchar](max) NULL,
    [InstanceNumber] [int] NULL,
    [Comment] [nvarchar](max) NULL,
    [InUse] [bit] NULL,
    [IsOtherSysType] [bit] NULL,
    [IsDeployed] [bit] NULL,
    [Exception] [nvarchar](max) NULL,
    [ReservationDate] [datetime2](7) NULL,
    [LastUpdated] [datetime2](7) NULL,
    [ReservatedBy] [int] NULL,
    [IsDeleted] [bit] NULL,
    [IsManuallyDefined] [bit] NULL,
    CONSTRAINT [PK_SIDGenerators] PRIMARY KEY CLUSTERED 
    (
        [Id] ASC
    ) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO

Answer 1

像這樣更改您的模型，或根據您的意願配置可為空的屬性。

public class SIDGenerator
{
    public int Id { get; set; }
    public string TrackId { get; set; }
    public string Track { get; set; }
    public string SId { get; set; }
    public int? InstanceNumber { get; set; }
    public string Comment { get; set; }
    public bool? InUse { get; set; }
    public bool? IsOtherSysType { get; set; }
    public bool? IsDeployed { get; set; }
    public string Exception { get; set; }
   
    public DateTime? ReservationDate { get; set; }
    public DateTime? LastUpdated { get; set; }
    public bool? IsDeleted { get; set; }
    public bool? IsManuallyDefined { get; set; }
    public int? ReservatedBy { get; set; }
}