Entity Framework code-first - cannot retrieve nested objects using include

Question

I am just starting to learn Entity Framework code-first. I am trying to use the .Include syntax to get related objects. I have been able to successfully retrieve objects into a list from a one to many relationship, but can't get it to work from a many to one relationship. So I have a song, which has a related orchestra and a related singer

The object definitions

public class Song
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }
    [ForeignKey("OrchestraId")]
    public Orchestra Orchestra { get; set; }
    public int OrchestraId { get; set; }
    [ForeignKey("SingerId")]
    public Singer Singer { get; set; }
    public int SingerId { get; set; }
    public int Genre { get; set; }
    public string Year { get; set; }

    public Song()
    {
        this.Orchestra = new Orchestra();
        this.Singer = new Singer();
    }
}

public class Singer
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Orchestra
{
    public int Id { get; set; }
    public string Name { get; set; }
}

I have a context object

public class POCContext : DbContext
{
    public DbSet<Singer> Singers { get; set; }
    public DbSet<Orchestra> Orchestras { get; set; }
    public DbSet<Song> Songs { get; set; }
}

The code I use to get a song is the following

    public Song GetSong(int songId)
    {
        Song song = new Song();

        song = _context.Songs.Include(s => s.Orchestra)
            .Include(s => s.Singer)
            .Single(s => s.Id == songId);
        return song;
    }

When I put a breakpoint on the return statement and look at the song, the song object is populated, but not the singer or orchestra objects.

I had a look at the following related question here but I have not been able to work out what I am doing wrong. Any help is greatly appreciated.

regards Carl

Does the song actually have related data in the db, is there Fk's, does it actually have data — TheGeneral, Aug 07 '18 at 03:48
Shortly, don't initialize non collection navigation properties like `Song.Orchestra` and `Song.Singer` with `new …` - there is a big chance that you mess up the EF processing. Remove the `Song` constructor and try again. Let me know to reopen the question if that's not the case. — Ivan Stoev, Aug 07 '18 at 09:01
Ivan Stoev, Thanks that fixed my issue. I didnt know enough to understand it was the initialization that was causing the problem! — Carl Skeen, Aug 07 '18 at 09:43

tymtam · Answer 1 · 2018-08-07T03:56:10.453

Orchestra and Singer should be virtual.

public virtual Orchestra Orchestra { get; set; }

public virtual Singer Singer { get; set; }

Here's a sample configuration:

public class Song
{
    [Key]
    public Guid Id { get; set; }

    public string Title { get; set; }

    //navigation property
    public virtual List<Singer> Singers { get; set; }
}


public class Singer
{
    [Key]
    public int Id { get; set; }

    [ForeignKey("Song")]
    [Required]
    public string SongId { get; set; }

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

    //navigation property
    public virtual Song Song { get; set; }
}

There is no *requirement* navigation properties to be `virtual`. — Ivan Stoev, Aug 07 '18 at 09:02

Entity Framework code-first - cannot retrieve nested objects using include

1 Answers1