Entity Framework with Repository Pattern, inserting data to tables with many-to-many relationship

I am trying to build a three tier architecture with BLL, DAL, and UI. I am working on a small Apartment Management System project (which includes the information about resident students, their rooms and the apartment of the rooms they stay). Since I am a beginner I have some technical problems I need to solve. I am using Entity Framework with repository pattern. My project is based on MVVM approach and I am using Automapper.

Codes for Automapper

public class AutoMapperProfile : Profile
{
    public AutoMapperProfile()
    {
        CreateMap<Room, RoomViewModel>().ReverseMap();
        CreateMap<Apartment, ApartmentViewModel>().ReverseMap();
    }
}

public class AutoMapperConfig
{
    public static void Configure()
    {
        Mapper.Initialize(x =>
        {
            x.AddProfile<AutoMapperProfile>();
        });
    }
}

I am trying to add a new room to my database. There is a many-to-many relationship between my Room and Apartment tables and my database looks like this:

My Database's screen shot

My IRepository interface looks like:

public interface IRepository<T> where T : class
{
    IEnumerable<T> GetAll();
    T GetById(int id);
    T Get(Expression<Func<T, bool>> expression);
    IQueryable<T> GetMany(Expression<Func<T, bool>> expression);
    bool Insert(T obj);
    bool Update(T obj);
    bool Delete(int id);
    int Count();
    void Save();
}

I have RoomRepository and ApartmentRepository, both implement IRepository interface. I have created my repositories and infrastructures:

Infrastructure (folder)

• IApartmentRepository.cs
• IRepository.cs
• IRoomRepository.cs
• IStudentRepository.cs
• IUserRepository.cs

Repository (folder)

• ApartmentRepository.cs
• RoomRepository.cs
• StudentRepository.cs
• UserRepository.cs

While adding a new Room, admin has to state to which apartment that room belongs. The Add method inside the RoomController is below:

[HttpPost]
    public JsonResult Add(RoomViewModel roomModel)
    {
        try
        {
            //var apartViewModel = new ApartmentRoomViewModel();
            //apartViewModel.ApartmentID = roomModel.ApartmentNameId;
            var room = AutoMapper.Mapper.Map<Room>(roomModel);
            var status = _roomRepository.Insert(room);
            _roomRepository.Save();
            //apartViewModel.RoomID = room.Id;

            return Json(new { status, message = "Ekleme işlemi başarılı." }, JsonRequestBehavior.AllowGet);
        }
        catch (Exception)
        {
            return Json(new { status = false, message = "Hata! Ekleme işlemi gerçekleştirilemedi." }, JsonRequestBehavior.AllowGet);
        }
    }

RoomViewModel

 public class RoomViewModel
{

    public int Id { get; set; }

    public int DoorNumber { get; set; }

    public int FloorNumber { get; set; }

    public int Capacity { get; set; }

    public int Fullness { get; set; }

    public string ApartmentName { get; set; }

    public int ApartmentNameId { get; set; }
}

UI

Room Add UI

My question is, when I want to insert the data I take from the user in the Room Add page, I can add the information gathered for the room to the Room table but I also want to add the apartment information (which is the ApartmentID of that apartment) of that room and the same room's RoomID to the ApartmentRoom table in the database and I couldn’t do that so far. If I’m not wrong so far, in that case what should I do?

1. Should I create another repository like ApartmentRoomRepository implementing IRepository interface and call the insert method of ApartmentRoomRepository in the Add method inside the RoomController? (This approach doesn’t seem like a correct one, as far as I understand but I’m not sure.)
2. Instead of the first option, should I create ApartmentRoomViewModel? In this case, how can I insert ApartmentID of the room with the room's RoomID to the ApartmentRoom table?

EDIT 1: I am using Database First approach.

EDIT 2: I have found the solution and shared as an answer below.

I have managed to find the solution. Firstly, I have added a single line to my AutoMapperProfile.cs file.

AutoMapperProfile.cs

 public class AutoMapperProfile : Profile
{
    public AutoMapperProfile()
    {
        CreateMap<Room, RoomViewModel>().ReverseMap();
        CreateMap<Apartment, ApartmentViewModel>().ReverseMap();

        // Added this new line
        CreateMap<ApartmentRoom, ApartmentRoomViewModel>().ReverseMap();
    }
}

public class AutoMapperConfig
{
    public static void Configure()
    {
        Mapper.Initialize(x =>
        {
            x.AddProfile<AutoMapperProfile>();
        });
    }
}

ApartmentRoom.cs

This class is already generated from my database.

public partial class ApartmentRoom
{
    public int Id { get; set; }
    public int ApartmentID { get; set; }
    public int RoomID { get; set; }

    public virtual Apartment Apartment { get; set; }
    public virtual Room Room { get; set; }
}

ApartmentRoomViewModel.cs

I have created this class.

public class ApartmentRoomViewModel
{
    public int ApartmentID { get; set; }
    public int RoomID { get; set; }
}

RoomController

I have changed the inside of RoomController a little. I have created an _entities object to be able to insert data into ApartmentRoom table.

public class RoomController : Controller
{
    ApartmentManSysEntities _entities = new ApartmentManSysEntities();
    private readonly IRoomRepository _roomRepository;
    private readonly IApartmentRepository _apartmentRepository;
    public RoomController(IRoomRepository roomRepository, IApartmentRepository apartmentRepository)
    {
        _roomRepository = roomRepository;
        _apartmentRepository = apartmentRepository;
    }

    [HttpPost]
    public JsonResult Add(RoomViewModel roomViewModel)
    {
        try
        {
            var room = AutoMapper.Mapper.Map<Room>(roomViewModel);
            if (_roomRepository.Insert(room))
            {
                _roomRepository.Save();
                var apartRoomViewModel = new ApartmentRoomViewModel
                {
                    ApartmentID = roomViewModel.ApartmentNameID,
                    RoomID = room.Id
                };
                var apartRoom = AutoMapper.Mapper.Map<ApartmentRoom>(apartRoomViewModel);
                _entities.ApartmentRoom.Add(apartRoom);
                _entities.SaveChanges();
            }
            else
            {
                return Json(new { status = false, message = "Hata! Ekleme işlemi gerçekleştirilemedi." }, JsonRequestBehavior.AllowGet);
            }
            return Json(new { status = true, message = "Ekleme işlemi başarılı." }, JsonRequestBehavior.AllowGet);
        }
        catch
        {
            return Json(new { status = false, message = "Hata! Ekleme işlemi gerçekleştirilemedi." }, JsonRequestBehavior.AllowGet);
        }
    }

}

After I added a new room into Room table, I called the last inserted room's Id value to make a new insert to ApartmentRoom table.

Result

ApartmentRoom table

Room table