解决code first Migration 增加外键时出现错误的问题

public class Comment
    {
        [Key]
        public int CommentId { get; set; }
        [Required]
        public int Star { get; set; }
        [Required]
        public string Content { get; set; }
        [Required]
        [MaxLength(30)]
        public string ProductName { get; set; }

        [Required]
        [ForeignKey("User")]
        public int UserId { get; set; }//需要增加的外键
        public virtual User User { get; set; }

    }

    public class User
    {
        [Key]
        public int UserId { get; set; }

        [Required(ErrorMessage = "该项为必填项")]
        [MaxLength(30, ErrorMessage = "请输入少于30个字符")]
        public string userName { get; set; }

        public virtual ICollection<Comment> Comment { get; set; }
    }

Add-Migration InitDB -Force
Update-Database -Verbose