如何通过外键关联自定义对象至User并解决属性显示异常问题

开发者阿泽

2026-6-21

问题：无法从关联外键表获取Department值并显示

我在显示自定义对象属性时遇到问题，程序无法从带有对应外键的表中获取关联的Department值，已经尝试过谷歌和YouTube上的空引用异常修复方案，但都无效。外键字段已填充，目标是显示关联的Department数据。

UserViewModel.cs

public class UserViewModel
{
    public string Name { get; set; }
    public string Id { get; set; }
    public Department Department { get; set; }
}

AppUser.cs

public class AppUser : IdentityUser
{
    [DefaultValue(null)]
    public string Name { get; set; }
    public Department Department { get; set; }
    public Single1 Single { get; set; }
}

Controller代码

public async Task<IActionResult> Index()
{
    
    IEnumerable<AppUser> users = await _userRepository.GetAll();
    List<UserViewModel> usersViewModel = new List<UserViewModel>();
    foreach (var user in users)
    {
        
        var userViewModel = new UserViewModel()
        {
            Id = user.Id,
            Name = user.Name,
            Department = await _userRepository.GetDepartmentByIdAsync(user.Department.DepartmentId),
        };
        usersViewModel.Add(userViewModel);
    }
    return View(usersViewModel);
}

Repository代码

public async Task<IEnumerable<AppUser>> GetAll()
{
    var users = await _context.Users.ToListAsync();
    return users;
}

public async Task<Department> GetDepartmentByIdAsync(string id)
{
    return await _context.Departments.Where(o => o.DepartmentId == id).FirstOrDefaultAsync();
}