[英]How to add value to a navigation property with Blazor and EF?
I have a reservation and a ship class for the DB with the Ship and Reservations navigation properties,我有一个带有 Ship 和 Reservations 导航属性的 DB 的预订和船类,
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; }
}
The DBcontext.cs file: 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; }
}
}
The reservationController.cs on the sever side: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();
}
The reservationService.cs on the client side:客户端的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;
}
And the razor page that uses this service:以及使用此服务的剃刀页面:
@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);
}
When I press the submit reservation button and the HandleSubmit function is called I got the following error: Microsoft.Data.SqlClient.SqlException (0x80131904): Cannot insert explicit value for identity column in table 'Ships' when IDENTITY_INSERT is set to OFF.
当我按下提交预订按钮并调用 HandleSubmit 函数时,我收到以下错误: Microsoft.Data.SqlClient.SqlException (0x80131904): Cannot insert explicit value for identity column in table 'Ships' when IDENTITY_INSERT is set to OFF.
So I tried this:所以我试过这个:
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; }
I also tried this modelBuilder.Entity<Reservation>().Property(a => a.Ship).ValueGeneratedNever();
我也试过这个modelBuilder.Entity<Reservation>().Property(a => a.Ship).ValueGeneratedNever();
But I got an error that said the ship is a navigation property so i cant use this function但是我收到一个错误,说这艘船是一个导航属性,所以我不能使用这个功能
Any ideas?有任何想法吗?
If I understood you correctly, then ship
id property is used as an index by EF by default naming convention, if you set it as code first.如果我理解正确,那么默认命名约定将ship
id 属性用作EF 的索引,如果您首先将其设置为代码。
I would try to set this property to a default value of it's kind (0 for int
, null
for string, etc) - it should allow EF to insert it into the database - this works if you want to actually add a ship
.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 将它插入到数据库中——如果你想实际添加一个ship
这可以工作。
If there is no ship in newly created entity, than just set ship to null
- should do the trick.如果新创建的实体中没有船,那么只需将船设置为null
- 应该可以解决问题。
我没有工作的原因是我试图在客户端为导航属性添加一个值,而您只能在服务器端执行此操作
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