Many-to-many relationship and multi select in asp.net core - entity-framework

Question

I'm trying to learn asp.net core with razor and I'm trying to make a videogame database to keep a track of finished games, games I haven't played yet, etc.
But I have a problem. I have a table Game and a table Developer. Since a game can have many developers and a developer can have many games y made a third table DeveloperXGame.
They are something like this
public class Game
{
public int Id { get; set; }
public string Name { get; set; }
}
public class Developer
{
public int Id { get; set; }
public string Name { get; set; }
}
public class DeveloperXGame
{
public int DeveloperId { get; set; }
public int JuegoId { get; set; }
public Developer Developer { get; set; }
public Game Game { get; set; }
}
public class ApplicationDbContext : DbContext
{
public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
: base(options)
{
}
public DbSet<Game> Game { get; set; }
public DbSet<Developer> Developer { get; set; }
public DbSet<DeveloperXGame> DeveloperXGame { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<DeveloperXGame>()
.HasKey(m => new { m.DeveloperId, m.GameId });
}
}
I already did the pages for the developers so I first create them manually. Now I'm trying to create the games and I want to show a select where I can select one or more developers of that list (next step will be to try to add them with ajax through the games page if they don't exists). But I'm lost beyond this point.
I don't know how to load the list of developers in that list and later on post how to save those selected items in the table DeveloperXGame.
Thanks

Answer 1

You can remove public DbSet<DeveloperXGame> DeveloperXGame { get; set; } from your context.
Index.cshtml.cs
public class IndexModel : PageModel
{
private readonly ApplicationDbContext _context;
public IndexModel(ApplicationDbContext context)
{
_context = context;
}
public Game Game { get; set; }
public IEnumerable<int> Developers { get; set; }
public IEnumerable<SelectListItem> DeveloperList { get; set; }
public IActionResult OnGet()
{
var developers = from m in _context.Developers
select m;
DeveloperList = developers.Select(m => new SelectListItem { Value = m.Id.ToString(), Text = m.Name });
return Page();
}
}
Here is the view Index.cshtml
#page
#model RazorPages.TestGame.Pages.Games.IndexModel
#{
ViewData["Title"] = "Index";
}
<div class="row">
<div class="col-md-4">
<form method="post">
<div class="form-group">
<label asp-for="Game.Name" class="control-label"></label>
<input asp-for="Game.Name" class="form-control" />
</div>
<div class="form-group">
<label asp-for="Developers" class="control-label"></label>
<select asp-for="Developers" asp-items="Model.DeveloperList">
<option value="">All</option>
</select>
</div>
<div class="form-group">
<input type="submit" value="Create" class="btn btn-default" />
</div>
</form>
</div>
You can also use ViewData to pass your developers list in your view. You can go through this sample web as in official doc here.Hope it helps you to get started!