Question

正如我在主题标题中所述，DataContext.SubmitChanges（）方法存在问题。我有两个表：用户和管理员（以及其他角色，例如Doctors等，但现在我正在使用这两个表）。这两个表的SQL脚本：用户：

`CREATE TABLE [dbo].[Users](
    [usrId] [int] IDENTITY(1,1) NOT NULL,
    [login] [nvarchar](50) NOT NULL,
    [password] [nvarchar](50) NOT NULL,
    [role] [char](3) NOT NULL,
    [staffId] [int] NOT NULL,
 CONSTRAINT [PK_Users] PRIMARY KEY CLUSTERED 
(
    [usrId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]`

对于管理员：

`CREATE TABLE [dbo].[Administrators](
    [adminId] [int] IDENTITY(1,1) NOT NULL,
    [name] [nvarchar](50) NOT NULL,
    [surname] [nvarchar](50) NOT NULL,
 CONSTRAINT [PK_Administrators] PRIMARY KEY CLUSTERED 
(
    [adminId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]`

现在，管理员在Administrators.adminId = Users.staffId上加入用户（adminId为PK，staffId为FK）。简单-我知道当User.staffId == Administrator.adminId AND User.role =“ ADM”时，表Users中的User是管理员。

那么探针在哪里？我为此数据库进行了LINQ映射：

[Database(Name = "BD_PROJ_GKiO3")]
public class BD_PROJ_GKiO3 : DataContext
{
    public Table<User> Users;
    public Table<Doctor> Doctors;
    public Table<LaboratoryWorker> LaboratoryWorkers;
    public Table<LaboratoryManager> LaboratoryManagers;
    public Table<Registrator> Registrators;
    public Table<Administrator> Administrators;
    public Table<Appointment> Appointments;
    public Table<ExaminationType> ExaminationTypes;
    public Table<LaboratoryExamination> LaboratoryExaminations;
    public Table<Patient> Patients;
    public Table<PhysicalExamination> PhysicalExaminations;

    public BD_PROJ_GKiO3(IDbConnection connection) : base(connection)
    {

    }
}

以及用户和管理员的映射：

[Table(Name = "Users")]
public class User
{
    //kolumna PK w tabeli Users
    [Column(IsPrimaryKey = true, IsDbGenerated = true, DbType = "Int NOT NULL IDENTITY")]
    public int usrId { get; set; }

    //Reszta kolumn
    [Column] public string login { get; set; }
    [Column] public string password { get; set; }
    [Column] public string role { get; set; }
    [Column] public string status { get; set; }
    [Column] public int staffId { get; set; }

    //Mapowanie relacji z tabelami aktorów
    private EntitySet<Doctor> _Doctors;
    [Association(Storage = "_Doctors", OtherKey = "docId", ThisKey = "staffId")]
    public EntitySet<Doctor> Doctors
    {
        get { return this._Doctors; }
        set { this._Doctors.Assign(value); }
    }

    private EntitySet<Registrator> _Registrators;
    [Association(Storage = "_Registrators", OtherKey = "registratorId", ThisKey = "staffId")]
    public EntitySet<Registrator> Registrators
    {
        get { return this._Registrators; }
        set { this._Registrators.Assign(value); }
    }

    private EntitySet<Administrator> _Administrators;
    [Association(Storage = "_Administrators", OtherKey = "adminId", ThisKey = "staffId", IsForeignKey = true)]
    public EntitySet<Administrator> Administrators
    {
        get { return this._Administrators; }
        set { this._Administrators.Assign(value); }
    }

    private EntitySet<LaboratoryManager> _LaboratoryManagers;
    [Association(Storage = "_LaboratoryManagers", OtherKey = "laboratoryPrincipalId", ThisKey = "staffId")]
    public EntitySet<LaboratoryManager> LaboratoryManagers
    {
        get { return this._LaboratoryManagers; }
        set { this._LaboratoryManagers.Assign(value); }
    }

    private EntitySet<LaboratoryWorker> _LaboratoryWorkers;
    [Association(Storage = "_LaboratoryWorkers", OtherKey = "laboratoryWorkerId", ThisKey = "staffId")]
    public EntitySet<LaboratoryWorker> LaboratoryWorkers
    {
        get { return this._LaboratoryWorkers; }
        set { this._LaboratoryWorkers.Assign(value); }
    }}


[Table(Name = "Administrators")]
public class Administrator
{
    //PK w tabeli Administrators
    [Column(IsPrimaryKey = true, IsDbGenerated = true)]
    public int adminId { get; set; }

    //Reszta kolumn
    [Column] public string name { get; set; }
    [Column] public string surname { get; set; }

    //Mapowanie relacji tabeli Administrators z tabelą Users
    private EntitySet<User> _Users;
    [Association(Storage = "_Users", OtherKey = "staffId", IsForeignKey = true, ThisKey = "adminId")]
    public EntitySet<User> Users
    {
        get { return this._Users; }
        set { this._Users.Assign(value); }
    }}

当然，这两个类都具有构造函数，但是我没有在这里粘贴它（当我必须这样做时，我会这样做）。

因此，在上面您可以看到我如何将表和关系从数据库映射到对象。

问题是当我尝试用表Administrators中的相关行更新表Users中的现有行时。我已经创建了用户实例（toUpdate），用于存储数据，并使用该表的行进行更新，接下来，我向其中添加一个管理员实例数据（admin）。首先-我正在获取DataContext对象，其次-我正在数据库中寻找供用户编辑的对象。

首先：

BD_PROJ_GKiO3 newDB = new BD_PROJ_GKiO3(Program.getConnection());
            User u = newDB.Users.SingleOrDefault(us => us.usrId == currentlyEdited.usrId);

找到了正确的用户（u），所以我正在尝试执行以下代码：

                            u.login = toUpdate.login;
                            u.role = toUpdate.role;
                            u.status = toUpdate.status;
                            u.staffId = toUpdate.staffId;
                            u.Administrators.ElementAt(0).name = admin.name;
                            u.Administrators.ElementAt(0).surname = admin.surname;
                            newDB.SubmitChanges();

在执行最后一行（newDB.SubmitChanges（））期间，抛出NullReferenceException。

堆栈跟踪：ExceptionStackTrace

在此先感谢所有尝试帮助我的人，我将非常感谢！编辑：我只是忘了提一下，我认为以这种方式创建和映射的数据库可能很好用，因为当我的应用程序启动时，我正在创建新的数据库作为程序的公共字段（应用程序根目录）并使用它，用户有可能登录，然后才能正常运行（登录时，我们必须检查用户和管理员的数据）。

每当我要更新连接的数据库时，DataContext.SubmitChanges（）都会引发NullReferenceException

0 个答案: