Net Core + EF Core + Sql Server

public class UsersInfo
    {
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]  //设置自增
        public int SeqNum { get; set; }
        [Key,MaxLength(50)]
        public string UserID { get; set; }
        //[Required]必填
        [Required,MaxLength(50)]
        public string UserName { get; set; }
        [MaxLength(1)]
        public int Gender { get; set; }
        [MaxLength(50)]
        public string BelongClass { get; set; }
        [MaxLength(255)]
        public string Disc { get; set; }
    }

public class DemoContext : DbContext
    {
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer(
                connectionString: "server=.;database=MyTestDB;uid=sjz2018dbuser;pwd=1ECD9E*#E9DCE1;"
            );
        }

        public DbSet<ClassInfo> ClassInfos { get; set; }
        public DbSet<UsersInfo> UsersInfos { get; set; }
    }