我正在使用.NET5，并使用EF Core和MSSQL作为数据库。
我有两个类，他们之间有很多对很多的关系。这些都是从模型迁移到数据库的。DB表示例
迁移：
migrationBuilder.CreateTable(
name: "TournamentUser",
columns: table => new
{
TournamentsId = table.Column<int>(type: "int", nullable: false),
UsersId = table.Column<int>(type: "int", nullable: false)
},
constraints: table =>
{
table.PrimaryKey("PK_TournamentUser", x => new { x.TournamentsId, x.UsersId });
table.ForeignKey(
name: "FK_TournamentUser_Tournaments_TournamentsId",
column: x => x.TournamentsId,
principalTable: "Tournaments",
principalColumn: "Id",
onDelete: ReferentialAction.Cascade);
table.ForeignKey(
name: "FK_TournamentUser_Users_UsersId",
column: x => x.UsersId,
principalTable: "Users",
principalColumn: "Id",
onDelete: ReferentialAction.Cascade);
});
型号：
public class Tournament
{
[Key]
public int Id { get; set; }
[Required, MaxLength(20)]
public string Name { get; set; }
[Required]
public int MaxPlayers { get; set; }
public int PlayersCount { get; set; }
[Required]
public DateTime Start { get; set; }
public bool IsStarted { get; set; }
public bool IsEnded { get; set; }
public List<User> Users { get; set; }
}
public class User
{
[Key]
public int Id { get; set; }
[Required, MaxLength(15)]
public string Username { get; set; }
[Required]
public string Password { get; set; }
[Required, MaxLength(20)]
public string Name { get; set; }
[Required, MaxLength(20)]
public string Surname { get; set; }
[JsonIgnore]
public List<Tournament> Tournaments { get; set; }
}
所以当我试图更新比赛模型
[HttpPut]
public async Task<ActionResult<Tournament>> Put([FromBody] Tournament tournament)
{
_context.Tournaments.Update(tournament);
await _context.SaveChangesAsync();
return CreatedAtAction(nameof(GetTournament), new { id = tournament.Id }, tournament);
}
我得到这个错误
Microsoft.Data.SqlClient.SqlException (0x80131904): Violation of PRIMARY KEY constraint 'PK_TournamentUser'. Cannot insert duplicate key in object 'dbo.TournamentUser'. The duplicate key value is (1, 1).
对此有什么可能的解决办法？我想保持我的多对多表UDPAT，因为每次更新锦标赛时，锦标赛的用户都可以被删除或添加。
可更新的锦标赛对象示例
如果要更新tournment,请尝试从torment对象中删除用户。
public async Task<ActionResult<Tournament>> Put([FromBody] Tournament tournament)
{
tournament.Users=null;
_context.Tournaments.Update(tournament);
await _context.SaveChangesAsync();
.....
}
或者如果您想将用户添加到您的锦标赛中
var existing= _context
.Tournaments
.Include(u=>u.Users)
.FirstOrDefault(t=> t.Id== tournament.Id);
if(existing==null) return ...error
if( existing.Users==null) existing.User=new List<User>();
if( existing.Users.Any(u=>u.Id=tournment.User.Id) return ...error
existing.Users.Add(tournment.User);
_context.Entry(existing).State = EntityState.Modified;
_context.SaveChanges();
它看起来很简单，但您为不显式添加多对多关系表而付出了代价。如果使用UserTournment表代码将更短。
你可以试试这个。我从没试过。如果有用，请告诉我：
var existing = _context
.Tournaments
.Include(u=>u.Users)
.FirstOrDefault(t=> t.Id== tournament.Id);
if(existing==null) return ...error
_context.Entry(existing).CurrentValues.SetValues(tournment);
_context.SaveChanges();
