ASP .NET Core MVC，Entity Framework，Identity——由外键组成的复合键

Question

我有以下 model 类。 我希望 TripId 和 TouristId 是出勤实体的复合键。

现在我在执行 sql 时收到此错误：

CREATE TABLE [Attendance] (
[Id] int NOT NULL IDENTITY,
[TouristId] nvarchar(450) NOT NULL,
[TripId] int NOT NULL,
CONSTRAINT [PK_Attendance] PRIMARY KEY ([Id]),
CONSTRAINT [FK_Attendance_AspNetUsers_TouristId] FOREIGN KEY ([TouristId]) REFERENCES [AspNetUsers] ([Id]) ON DELETE CASCADE,
CONSTRAINT [FK_Attendance_Trip_TripId] FOREIGN KEY ([TripId]) REFERENCES [Trip] ([Id]) ON DELETE CASCADE);

在表 'Attendance' 上引入 FOREIGN KEY 约束 'FK_Attendance_Trip_TripId' 可能会导致循环或多个级联路径。 指定 ON DELETE NO ACTION 或 ON UPDATE NO ACTION，或修改其他 FOREIGN KEY 约束。 无法创建约束或索引。 请参阅以前的错误。

public class Attendance
    {
        public virtual Trip Trip { get; set; }
        public virtual ApplicationUser Tourist { get; set; }
    }

public class ApplicationUser : IdentityUser
    { 
    
        [PersonalData]
        [Column(TypeName = "nvarchar(MAX)")]
        public string FirstName { get; set; }
        [PersonalData]
        [Column(TypeName = "nvarchar(MAX)")]
        public string Surname { get; set; }

        [PersonalData]
        [Column(TypeName = "nvarchar(MAX)")]
        public string BirthDate { get; set; }
    }

public class Trip
    {
        public int TripId { get; set; }
        public string TripDate { get; set; }
        public int TripDuration { get; set; }
        public int TripLength { get; set; }
        public int TripSeats { get; set; }
        public Trail Trail { get; set; }
        public ApplicationUser Guide { get; set; }
    }

编辑：

public class Attendance
    {
        public int AttendanceId { get; set; }
        public int? TripId { get; set; }
        public int? TouristId { get; set; }
        public virtual Trip Trip { get; set; }
        public virtual ApplicationUser Tourist { get; set; }
    }

但是外键仍然设置为“NOT NULL”。

Answer 1

在DbContext class 进入OnModelCreating覆盖执行以下操作：

modelBuilder.Entity<Attendance>()
.HasOne(p => p.Tourist)
.WithMany<ApplicationUser>()
.OnDelete(DeleteBehavior.Cascade `or` DeleteBehavior.Restrict);