Entity Framework Foreign Key restraint

_appointmentContext.SaveChanges();

    public class AppointmentDbContext : DbContext
    {
        public DbSet<Appointment> Appointments { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            // Set the file location for the patient database
            optionsBuilder.UseSqlite("Data Source=appointment.db");
        }
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Appointment>()
                .HasOne(a => a.Patient)
                .WithMany(p => p.Appointments) // Matches Patient.Appointments
                .HasForeignKey(a => a.PatientId)
                .OnDelete(DeleteBehavior.Cascade);

            modelBuilder.Entity<Appointment>()
                .HasOne(a => a.User)
                .WithMany() 
                .HasForeignKey(a => a.UserId)
                .OnDelete(DeleteBehavior.Restrict);
        }

        public enum AppointmentStatus 
        {
            Completed = 1,
            Scheduled = 2,
            Cancelled = 3,


        } //UserAccountType

        public class Appointment
        {
            public int Id { get; set; }
            public DateTime Scheduled { get; set; }
            public AppointmentStatus Status { get; set; }

            //navigation properties 
            public int PatientId { get; set; }
            public Patient Patient { get; set; }
            public int UserId { get; set; }
            public User User { get; set; }
        }
    }
}