How to retrieve data from the database using ASP.NET MVC

Question

I have two models/tables, one is User and the other is role the relationship is one Role can have many users. I am trying to loop through the data in the user model navigation property but i am getting an error that its returning null.

User model

public class User
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int User_Id { get; set; }

    [Required]
    [Display(Name ="User Name")]
    public string User_Name { get; set; }

    [Required(ErrorMessage = "The Field Is Required")]
    [MaxLength(10, ErrorMessage = " Please Enter A Valid Input")]
    public string Password { get; set; }

    //Nav

    [ForeignKey("RoleId")]
    [Display(Name ="User Role:")]
    public int RoleId { get; set;}

    public Role Role { get; set; }
}

Role Model

public class Role
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int  Role_id { get; set; }

    [Required(ErrorMessage ="This field is required")]
    [Display(Name ="Role Name :")]
    public string RoleType { get; set; }
    
    //nav
    public List<User> Users { get; set; }

}

Controller action Method:

public async Task<IActionResult> Index()
        {
            var viewModel = await userRepository.GetAllUsersAlongWithRolesAsync();

            //var viewModel = await baseRepository.GetAllObjectsAsync();

            return View("Index",viewModel);
        }

Updates: UserRepository that inherited from the IBaseRepository

public class UserRepository : BaseRepository<User>, IUserRepository
{
    private readonly ApplicationDbContext _Context;

    public UserRepository(ApplicationDbContext context):base (context)
    {
        _Context = context;
    }

    public async Task <IEnumerable<User>> GetAllUsersAlongWithRolesAsync()
    {
        var getUsers = await _Context.Users.Include(u => u.Role).ToListAsync();

        return getUsers;
    }
}

In the User controller for injecting:

// injection
private readonly IBaseRepository<User> baseRepository;

private readonly IBaseRepository<Role> roleRepository;

private readonly IUserRepository userRepository;

public UserController(IBaseRepository<User> _baseRepository, IBaseRepository<Role> _roleRepository, IUserRepository userRepository)
{
    baseRepository = _baseRepository;
    this.roleRepository = _roleRepository;
    this.userRepository = userRepository;
}

Did you checked the role if that exist? This the screenshot is for view can you please share the related controller details? — Md Farid Uddin Kiron
– Md Farid Uddin Kiron, Commented Jan 7, 2022 at 7:43
How (in code) did you load the user to be displayed in that view? Did you use .Include(u => u.Role) to also load the Role object with all its properties? — marc_s
– marc_s, Commented Jan 7, 2022 at 8:04
where i suppose to write this line of code and i guess that's the answer — Hesham Eldawy
– Hesham Eldawy, Commented Jan 7, 2022 at 8:05
Your code is still very much incomplete - can't really tell what you're doing, and what might be the cause for the error. Basically, somewhere you need something like : User myUser = dbContext.User.Where(u => u.Id == id)?.Include(u => u.Role); or something like that - you need to explicitly call .Include to load the dependent property - all the code I've seen so far to does NOT do that and thus your myUser.Role will be NULL .... — marc_s
– marc_s, Commented Jan 7, 2022 at 8:51

marc_s · Accepted Answer · 2022-01-08 06:53:27Z

2

Since your method GetAllObjectsAsync is so generic, you probably won't be able to add the .Include() you need.

I'd suggest a separate method GetAllUsers() to your repository - possibly the concrete UserRepository, if you have that:

public async Task<IEnumerable<User>> GetAllUsersAsync()
{
    var getUsers = await _Context.Users.Include(u => u.Role).ToListAsync();

    return getUsers;
}

answered Jan 8, 2022 at 6:53

marc_s

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5 Comments

Hesham Eldawy Over a year ago

first thanks so much for your answer and it seems correct but i got another error this is the error title

InvalidOperationException: Unable to resolve service for type 'Interfaces.IUserRepository' while attempting to activate 'InventoryManagmentSystem.Controllers.UserController'.

Hesham Eldawy Over a year ago

I updated the code can u check it if u got time, i think it's about when i inject IUserRepository

marc_s Over a year ago

@HeshamEldawy: most likely, you haven't added a service registration for IUserRepository to your startup class (for .NET Core - or whatever DI repo you're using), so the dependency injection system can't find what concrete class to use for IUserRepository when injecting dependencies.

Hesham Eldawy Over a year ago

okay i am sorry still didn't get what u are trying to say but what's your recommendation to solve the problem. i injected the IUserRepository correctly i think

marc_s Over a year ago

@HeshamEldawy: yes, you injected it correctly - but the DI container (either in .NET Core, or any other DI container you might be using) doesn't know about IUserRepository yet. Somewhere, you must be configuring/defining your DI container - there, you need to add the registration for "use UserRepository whenever someone asks for the IUserRepository interface")

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