EF加载相关数据问题 [英] EF loading related data issue

问题描述

我有两个实体:

public class Album
{
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    public virtual int GenreId { get; set; }
    public virtual int ArtistId { get; set; }
    public virtual string CoverURL { get; set; }
    public virtual int Cost { get; set; }
    public virtual Artist Artist { get; set; }
    public virtual Genre Genre { get; set; }
}

public class Genre
{
    public int Id { get; set; }       
    public string Name { get; set; }
    public virtual IEnumerable<Album> Albums{get;set;}
    public int AlbumCount { get { return Albums.Count(); } }
    public Genre()
    {
        Albums = new List<Album>();
    }
}

这是控制器的动作.

public ActionResult Index()
    {
        var genres = db.Genres.ToList();
        return View(genres);
    }

我在流派和专辑之间有一对多的映射关系(一个专辑只能有一个流派，但是一个流派可以属于多个专辑).当我尝试获取专辑详细信息(包括类型的导航属性)时，它为我提供了预期的数据.但是，当我尝试显示所有流派时，总会给我0作为专辑计数.我怀疑有约束力的问题，但我无法找出问题所在.如果您能帮助您找出问题，将非常高兴.

I've one to many mapping between Genre and Album( A album can have only one genre, but a genre can belong to multiple albums). When i try to fetch Album details(including genre nav. property) it gives me expected data. But when i try to display all genres it always gives me 0 as album count. I suspect a binding issue, but i'm unable to find out where. Would be glad if you can help find out the issue.

推荐答案

对于导航属性，您必须使用 ICollection 而不是 IEnumerable :

You must use ICollection instead of IEnumerable for your navigation properties :

public virtual ICollection<Album> Albums { get; set; }

(例如，请参见此 SO答案)

然后，您可以使用 Include 方法通过 Genres 获取相册:

Then you can use the Include method to fetch Albums with Genres :

db.Genres.Include(genre => genre.Albums)

或

db.Genres.Include("Albums")

阅读此

EDIT : read this SO answer for more informations about collection types. Basically, ICollection inherits from IEnumerable, and allows you to modify your collection (IEnumerable's main purpose is iteration).

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