1:(0or1)

public class User
   {
      public int ID { get; set; }

      public string UserName { get; set; }

      public string Passwd { get; set; }

      public virtual UserInfo UserInfo { get; set; }

   }

public class UserInfo
    {
        public int ID { get; set; }

        public string Name { get; set; }

        public string  Phone { get; set; }

        public virtual User User { get; set; }

        public int UserID { get; set; }

    }

//
            modelBuilder.Entity<User>().ToTable("Users");
            modelBuilder.Entity<User>().HasKey(u => u.ID);

            modelBuilder.Entity<UserInfo>().ToTable("UserInfos");
            modelBuilder.Entity<UserInfo>().HasKey(b => b.ID);

            ////针对“用户不一定要有信息类，信息一定要有用户类”关系的设置
            modelBuilder.Entity<User>().HasOptional(b => b.UserInfo)
                .WithRequired(x => x.User);