Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

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
231,269 Points
Steven Parker
Steven Parker
231,269 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
231,269 Points
Steven Parker
Steven Parker
231,269 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();
}