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C# Entity Framework Basics LINQ Queries Loading Related Entities

Alex Hedley
Alex Hedley
16,381 Points
Posted by Alex Hedley
Alex Hedley
16,381 Points

Load Artists for ComicBook

In program.cs there is a method

private static void ListComicBook(int comicBookId)

This loads the comicbook then loops the Artists:

ComicBook comicBook = Repository.GetComicBook(comicBookId);

foreach (ComicBookArtist artist in comicBook.Artists)
{
    ConsoleHelper.OutputLine("{0} - {1}", artist.Artist.Name, artist.Role.Name);
}

If we wanted to add a Repository method to return a List of Artists can this be done in Linq?

public IEnumerable<Artist> GetArtistsForComicBook(int comicBookId)

We have

return context.ComicBooks
    .Include(cb => cb.Artists)
    .Where(cb => cb.Id == comicBookId)
    .SingleOrDefault();

Can you make a Select to just return the cb.Artists.Artist List Since cb.Artists is a ComicBookArtist and I actually want a List of Artist

1 Answer

Steven Parker
Steven Parker
231,268 Points
Steven Parker
Steven Parker
231,268 Points

I believe you can do this with a one-liner.

You don't need LINQ just to get a list:

    return Repository.GetComicBook(comicBookId).Artists.ToList();
Alex Hedley
Alex Hedley
16,381 Points
Alex Hedley
Alex Hedley
16,381 Points

I'm getting the following error at first go, but I'll look into it

Cannot implicitly convert type 'System.Collections.Generic.List<ComicBookLibraryManager.Models.ComicBookArtist>' to 'System.Collections.Generic.IEnumerable<ComicBookLibraryManager.Models.Artist>'. An explicit conversion exists (are you missing a cast?)

Steven Parker
Steven Parker
231,268 Points
Steven Parker
Steven Parker
231,268 Points

You could cast the result, or just define the method to return a list:

public List<Artist> GetArtistsForComicBook(int comicBookId)
{
    return Repository.GetComicBook(comicBookId).Artists.ToList();
}