Question

我定义了以下POCO类，它们以多对多的关系将演讲者映射到主题：

public class Speaker
{
        public int Id { get; set; }
        public string Firstname { get; set; }
        public string Surname { get; set; }

        public virtual ICollection<SpeakerTalkTheme> TalkThemes { get;set; }
}

public class SpeakerTalkTheme
    {
        [Key, Column(Order = 0)]
        public int TalkThemeId { get; set; }

        [Key, Column(Order = 1)]
        public int SpeakerId { get; set; }

        public TalkTheme TalkTheme { get; set; }


        public Speaker Speaker { get; set; }
    }
}   

public class TalkTheme
    {
        public int Id { get; set; }
        public string Theme { get; set; }

        public int Length { get; set; }

        public virtual ICollection<ThemeTag> ThemeTags { get; set; }
        public virtual ICollection<SpeakerTalkTheme> TalkThemes { get;set; }
    }

但是，当我查询数据库并从WebAPI返回时：

 public class SpeakerController : ApiController
    {
        public IEnumerable<Speaker> Get()
        {
            var db = new MyDbContext();
            var model = db.Speakers.Include(x => x.TalkThemes).ToList();
            return model;
        }     
    }

我在themes属性中得到NULL（见下文）：

[
  {
    "TalkThemes": [
      {
        "TalkThemeId": 1,
        "SpeakerId": 1,
        "TalkTheme": null
      }
    ],
    "Id": 1,
    "Firstname": "Joe",
    "Surname": "Bloggs"
  }
]

不应填充TalkTheme属性吗？它目前只显示NULL，我不知道如何填充这个。

Answer 1

因为你需要加载另一个级别。在Include电话中执行以下操作：

 //...
 var model = db.Speakers.Include(x => x.TalkThemes.Select(tt=>tt.TalkTheme )).ToList();

如果您想查看有关如何在查询中加载多个级别的更多示例，请查看此msdn page中的备注部分。

EF6没有填充多对多的财产

1 个答案: