EF loading related data issue

Question

I've two entities:

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>();
    }
}

and here is the controller action.

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

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.

Community · Accepted Answer · 2017-05-23 11:56:47Z

2

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

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

(See this SO answer for example)

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

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

or

db.Genres.Include("Albums")

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).

edited May 23, 2017 at 11:56

CommunityBot

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answered Dec 30, 2013 at 12:08

Réda Mattar

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1 Comment

Ashish Charan Over a year ago

Thanks. This works. I'm new to MVC & EF. Could you please throw some light on ICollection and IEnumerable?

andreasnico · Accepted Answer · 2013-12-30 11:45:18Z

0

Have you tried this?

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

answered Dec 30, 2013 at 11:45

andreasnico

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5 Comments

Ashish Charan Over a year ago

Yup tried this. But it gives me syntax error. Possibly the EF framework I'm using doesn't support this. It expects a "string path" as argument.

andreasnico Over a year ago

Have you tried with a string? Like this: var genres = db.Genres.Include("Albums").ToList();

Ashish Charan Over a year ago

A specified Include path is not valid. The EntityType 'MvcMusicStore.DAL.Genre' does not declare a navigation property with the name 'Albums'. This error comes.

andreasnico Over a year ago

Have you configured your modelbuilder correct? Something like this: modelBuilder.Entity<Genres>() .HasMany(x => x.Albums) Read more here: msdn.microsoft.com/en-us/data/jj591620.aspx

Ashish Charan Over a year ago

No I've not configured. Is it necessary?

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