我有兩個班級聯系人和組結合FirstName和LastName必須是唯一的，可以為單個聯系人添加多個地址。如何在實體框架代碼優先方法中做到這一點？public class Contacts{    [Key]    public int ContactID { get; set; }    [ForeignKey("Group")]    public int GroupID { get; set; }    [Required]    public string FirstName { get; set; }    [Required]    public string LastName { get; set; }    [Required]    public string Address { get; set; }    [Required]    public string Number { get; set; }    [Required]    [EmailAddress]    public string EmailId { get; set; }    [DataType(DataType.Date)]    public DateTime CreateDate { get; set; }    public DateTime? ModifiedDate { get; set; }    public virtual Groups Group { get; set; }}public class Groups{    [Key]    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]    public int GroupID { get; set; }    [Required]    public string GroupName { get; set; }    [Required]    public string GroupDiscription { get; set; }    public DateTime CreateDate { get; set; }    public DateTime ModifiedDate { get; set; }}