实体框架 - DbSet中的集合

Question

我想在User类中创建用户集合，但EF返回失败＆＃34;违反了Multiplicity约束。＆＃34;

[Table("Users")]
public class UsersDbSet
{
    public UsersDbSet()
    {
        Friends = new List<UsersDbSet>();
    }

    [Key, Required, DatabaseGenerated(DatabaseGeneratedOption.Identity), Index(IsUnique = true)]
    public int UserID { get; set; }

    [Required, Index(IsUnique = true), MaxLength(MaxLoginLength)]
    public string Login { get; set; }

    [Required]
    public string Password { get; set; }

    public virtual ICollection<UsersDbSet> Friends { get; set; }
}

我不知道问题出在哪里......