ASP.NET MVC如何访问Entity Framework生成的外键？

Question

Song has a many to many relationship with it's self. I store these ids in a class called SimilarVersion with both id columns.

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

    public string AudioName { get; set; }

    public string ArtistName { get; set; }

    ...

    public virtual ICollection<SimilarVersion> SimilarVersions { get; set; } = new List<SimilarVersion>();      
}

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

    public int? Song_Id1 { get; set; }
}

View Models:

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

    public string AudioName { get; set; }

    public string ArtistName { get; set; }

    ...

    public ICollection<SimilarSongDto> SimilarSongDtos { get; set; } = new List<SimilarSongDto>();
}

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

    public string AudioName { get; set; }

    public string ArtistName { get; set; }

    ...
}

The SimilarVersion table in my database now has Id , Song_Id , Song_Id1 , as EF has generated Song_Id. How do I get to use that EF generated column in my code though?

_similarVersionService.GetSimiliarVersion().Song_Id will give me an error because there is no property in the class called that. I could manually add it to the class like I have done with Song_Id1 and remove the collection from the other class but I think I must be doing something wrong. Also please tell me if there is a better way of mapping this.

I tried adding public int Song_Id { get; set; } public int Song_Id { get; set; } public int Song_Id { get; set; } and it just made another column in my table called Song_Id2 .

public ActionResult Song(int id)
{
    //Map the domainModel to songViewModel
    var songDto = Mapper.Map<Song, SongDto>(_songService.GetSong(id));

    //Get all of the songs where the id == the Song_Id column in similar version table
    var songs = _songService.GetSongs().ToList()
                .Where(x => x.SimilarVersions.Any(z => z.Song_Id == songDto.Id))
                .ToList(); //z.Song_Id no definition found

    //Map the Song domain to SimilarSong ViewModel and assign it to the songDto to be passed to the view
    songDto.SimilarSongDtos = Mapper.Map<ICollection<Song>, ICollection<SimilarSongDto>>(songs);

    return View(songDto);
}

Edit. Trying to add to a row based on Admir answer:

var songToUpload = new Song
{
    AudioName = uploadSongDtos[i].AudioName.Trim(),
    ArtistName = uploadSongDtos[i].ArtistName,                        
};

 foreach (var compareAgainstString in _songService.GetSongs().ToDictionary(x => x.Id, x => x.AudioName))
 {
       var score = SearchContext.Levenshtein.iLD(songToUpload.AudioName, compareAgainstString.Value);

       //Don't add the current song
       if (score < 50 && songToUpload.Id != compareAgainstString.Key)
           songToUpload.SimilarVersionsWhereSimilar.Add(new SimilarVersion { SimilarId = compareAgainstString.Key });
 }

Both OriginalId and SimilarId are assigned to whatever the id of songToUpload.Id is given the relationship we defined in models, which is correct for OriginalId but it is also overriding my custom set SimilarId above. How can I stop this?

Answer 1

It is likely the ID is actually generated by your Store. Call Context.SaveChanges() to create it, then read the ID.

Answer 2

You can take this approach:

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

    public string ArtistName { get; set; }

    public virtual IList<Similarity> SimilaritiesWhereOriginal { get; set; }

    public virtual IList<Similarity> SimilaritiesWhereSimilar { get; set; } 
}

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

    public int OriginalId { get; set; }
    public virtual Song Original { get; set; }

    public int SimilarId { get; set; }
    public virtual Song Similar { get; set; }
}

public class ApplicationDbContext : DbContext
{
    public DbSet<Song> Songs { get; set; }

    public DbSet<Similarity> Similarities { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Song>().HasMany(x => x.SimilaritiesWhereOriginal).WithRequired(x => x.Original).WillCascadeOnDelete(false);
        modelBuilder.Entity<Song>().HasMany(x => x.SimilaritiesWhereSimilar).WithRequired(x => x.Similar).WillCascadeOnDelete(false);
        base.OnModelCreating(modelBuilder);
    }
}

Similarity class shows relationship between "original" song and "similar" song. This class replaces EF auto-generated table with your own many-2-many relationship table that you can access from the code.