如何使用 Blazor 和 EF 為導航屬性增加價值？

Question

我有一個帶有 Ship 和 Reservations 導航屬性的 DB 的預訂和船類，

    public class Reservation {
        public Reservation() {
            Ship = new Ship();
        }
        public int Id { get; set; }
        public DateTime FromDate { get; set; }
        public DateTime ToDate { get; set; }
        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; }
    }

DBcontext.cs 文件：

        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);
        }

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

服務器端的reservationController.cs：

        [HttpPost]
        public async Task<IActionResult> CreateReservation(ReservationGetDTO reservationDTO) {
            _context.Reservations.Add(Mapper.Map(reservationDTO, new Reservation()));
            await _context.SaveChangesAsync();
            return await GetReservations();
        }

客戶端的reservationService.cs：

        public async Task<List<ReservationGetDTO>> CreateReservation(ReservationPostDTO reserv) {
            var result = await _httpClient.PostAsJsonAsync("api/reservations", reserv);
            reservations = await result.Content.ReadFromJsonAsync<List<ReservationGetDTO>>();
            return reservations;
        }

以及使用此服務的剃刀頁面：

@code {
    [Parameter]
    public ShipDTO SelectedShip { get; set; }

    private ReservationPostDTO reservation = new ReservationPostDTO {
        FromDate = DateTime.Today,
        ToDate = DateTime.Today.AddDays(1),
    };

    async void HandleSubmit() {
        reservation.Ship = SelectedShip;
        await ReservationService.CreateReservation(reservation);
    }

當我按下提交預訂按鈕並調用 HandleSubmit 函數時，我收到以下錯誤： Microsoft.Data.SqlClient.SqlException (0x80131904): Cannot insert explicit value for identity column in table 'Ships' when IDENTITY_INSERT is set to OFF. 所以我試過這個：

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");
        }
//I also tried to put this annotation to the Ship
[DatabaseGenerated(DatabaseGeneratedOption.None)]
        public Ship Ship { get; set; }

我也試過這個modelBuilder.Entity<Reservation>().Property(a => a.Ship).ValueGeneratedNever(); 但是我收到一個錯誤，說這艘船是一個導航屬性，所以我不能使用這個功能

有任何想法嗎？

Answer 1

如果我理解正確，那么默認命名約定將ship id 屬性用作EF 的索引，如果您首先將其設置為代碼。
我會嘗試將此屬性設置為其類型的默認值（0 表示int ， null表示字符串等）——它應該允許 EF 將它插入到數據庫中——如果你想實際添加一個ship這可以工作。
如果新創建的實體中沒有船，那么只需將船設置為null - 應該可以解決問題。

Answer 2

我沒有工作的原因是我試圖在客戶端為導航屬性添加一個值，而您只能在服務器端執行此操作