c# - 插入数据库一对多关系.net core 3.1

Question

我有表 Race 和 Subrace 的一对多关系。1 个种族可以有多个子种族，但 1 个子种族只能是 1 个种族。我做了以下课程。

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

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

        [Required]
        [StringLength(200)]
        public string RaceFeatures { get; set; }


        [JsonIgnore]
        public IList<SubRace> SubRaces { get; set; }

 public class SubRace
    {
        public int Id { get; set; }

        [Required]
        [StringLength(50, ErrorMessage = "Only 50 characters allowed")]
        public string SubRaceName { get; set; }
        [Required]
        [StringLength(400, ErrorMessage = "Only 400 characters allowed")]
        public string SubraceFeatures { get; set; }



        public int RaceID { get; set; }
        public Race Race { get; set; }
    }

但是，我无法弄清楚我必须如何初始化此表中的值。这是我正在尝试做的，但在尝试运行时出现以下错误。

System.NullReferenceException：“对象引用未设置为对象的实例。”

API.Model.Race.SubRaces.get 返回 null。

if (!context.Races.Any())
            {
                var rc0 = new Race()
                {
                    RaceName = "Elf",
                    RaceFeatures = "Darkvision. +2 Charisma",
                  
                };
                var sr1 = new SubRace()
                {
                    Race = rc0,
                    SubRaceName = "Wood",
                    SubraceFeatures = "+1 Wisdom",

                };
                rc0.SubRaces.Add(sr1);
                context.Races.Add(rc0);
                context.SaveChanges();
            }

我在这里做错了什么？我似乎无法弄清楚。

标签： c#asp.netentity-frameworkapidbcontext

Answer 1

您缺少 SubRaces 初始化。

var rc0 = new Race()
            {
                RaceName = "Elf",
                RaceFeatures = "Darkvision. +2 Charisma",
                SubRaces = new List<SubRace>()
            };