如何使用 Blazor 和 EF 为导航属性添加值？

Question

我有一个预订和一艘船 class 具有船舶和预订导航属性的数据库，

    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; }
    }
}

服务器端的reservationController.cs：

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

客户端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;
        }

以及使用该服务的razor页面：

@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);
    }

当我按下提交预订按钮并调用 HandleSubmit 函数时，出现以下错误：Microsoft.Data.SqlClient.SqlException (0x80131904): Cannot insert explicit value for identity column in table 'Ships' when IDENTITY_INSERT is set to OFF. 所以我尝试了这个：

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; }

我也试过这个modelBuilder.Entity<Reservation>().Property(a => a.Ship).ValueGeneratedNever();但是我得到一个错误说这艘船是导航属性所以我不能使用这个功能

有什么想法吗？

Answer 1

如果我没理解错的话，如果您首先将其设置为代码，则 ship id 属性会被 EF 默认用作索引。
我会尝试将此属性设置为其类型的默认值（0 表示 int，null 表示字符串等）——它应该允许 EF 将其插入数据库——这有效如果你想实际添加一个 ship.
如果新创建的实体中没有飞船，则只需将飞船设置为 null - 应该可以解决问题。

Answer 2

我没有工作的原因是我试图在客户端向导航属性添加一个值，而这只能在服务器端进行

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