"NameOfProperty" cannot be used as a property on entity type 'NameOfType' because it is configured as a navigation

Question

I have a reservation and a ship class for the DB with the Ship and Reservations navigation properties,

    public class Reservation {
        public Reservation() {
            Ship = new Ship();
        }
        public int Id { get; set; }
        public DateTime FromDate { get; set; }
        public DateTime ToDate { get; set; }
       [DatabaseGenerated(DatabaseGeneratedOption.None)]
        public Ship Ship { get; set; }
   }

    public class Ship {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Port{ get; set; }
        public List<Reservation> Reservations { get; set; }
    }

The DBcontext.cs file:

        protected override void OnModelCreating(ModelBuilder modelBuilder) {
            base.OnModelCreating(modelBuilder);
            modelBuilder.Entity<Reservation>().HasOne(r => r.Ship).WithMany(s => s.Reservations);
            modelBuilder.Entity<Reservation>().HasOne(u => u.Person).WithMany(r => r.Reservations);
            modelBuilder.Entity<Ship>().HasMany(res => res.Reservations).WithOne(s => s.Ship);

            //This line generates the error
            modelBuilder.Entity<Reservation>().Property(a => a.Ship).ValueGeneratedNever();
        }

        public DbSet<Reservation> Reservations { get; set; }
        public DbSet<Ship> Ships { get; set; }
    }
}

The reason why I added this line that generates the error and the executeSqlRawAsync methods below is that I tried to solve this error: Microsoft.Data.SqlClient.SqlException (0x80131904): Cannot insert explicit value for identity column in table 'Ships' when IDENTITY_INSERT is set to OFF.` I want to create a reservation in the DB with a ship in it but I can not insert a value. So I tried fix it with this ValueGeneragtedNever method and the executeRawSql methods but it gives me the error in the title.

public async Task CreateReservation(ReservationGetDTO reservationDTO)
        {
            await _context.Database.ExecuteSqlRawAsync("SET IDENTITY_INSERT [dbo].[Reservations] ON");
            _context.Reservations.Add(Mapper.Map(reservationDTO, new Reservation()));
            await _context.SaveChangesAsync();
            await _context.Database.ExecuteSqlRawAsync("SET IDENTITY_INSERT [dbo].[Reservations] OFF");
        }

Any ideas what did I miss?

Answer 1

fix the reservation class , remove [DatabaseGenerated(DatabaseGeneratedOption.None)] and constructor

public class Reservation {
       
        public int Id { get; set; }
        public DateTime FromDate { get; set; }
        public DateTime ToDate { get; set; }

        public int ShipId { get; set; }
        public virtual  Ship Ship { get; set; }
   }

    public class Ship {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Port{ get; set; }
        public virtual  ICollection<Reservation> Reservations { get; set; }
    }

and since you are using ef core 5+ remove all fluent API from dbcontext, you don't need them

and try to add a new item using this code

public async Task CreateReservation(ReservationGetDTO reservationDTO)
        {
           
          _context.Reservations.Add(Mapper.Map(reservationDTO, new Reservation()));
            await _context.SaveChangesAsync();
           
        }

Answer 2

Another reason why this did not work was that I tried to add value to the navigation property on the client side after pressing the submit button. But you only can add value to a navigation property on the server side.