Terrykk Terrykk - 1 month ago 10
C# Question

Entity Framework - list of items is not loading

I'm trying to save games in database with EntityFramework Code-First.

There are fragments of my classes:

/// <summary>
/// Game class
/// </summary>
public class Game : ObservableObject
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int GameId { get; set; }

/// <summary>
/// List of teams
/// <see cref="Models.Teams"/>
/// </summary>
public Teams Teams
{
get
{
return teams;
}
set
{
teams = value;
OnPropertyChanged("Teams");
}
}
}


/// <summary>
/// Teams class
/// </summary>
public class Teams : ObservableObject, IEnumerable<Team>
{
public int GameId { get; set; }

public Game Game { get; set;}

List<Team> teamsList = new List<Team>();

/// <summary>
/// List of teams
/// </summary>
public List<Team> TeamsList
{
get
{
return teamsList;
}
set
{
teamsList = value;
OnPropertyChanged("TeamsList");
}
}
}

/// <summary>
/// Team (group of players)
/// </summary>
public class Team : ObservableObject
{


#region Properties & fields

List<Player> players = null;
static int NumberOfTeams = 0;

/// <summary>
/// List of players in team
/// </summary>
public List<Player> Players
{
get
{
return players;
}
set
{
players = value;

OnPropertyChanged("NumberOfPlayers");
OnPropertyChanged("IsEmpty");
OnPropertyChanged("IsNotDefault");
OnPropertyChanged("Players");
}
}
}

/// <summary>
///Defines player
/// </summary>
public class Player : Models.Person
{

/// <summary>
/// Identifies player in game. Also lets to recover player's statistics from last month
/// </summary>
public int PlayerId { get; set; }
}


And the Entity Framework part:

public class GameContext : DbContext
{
public GameContext() : base("Db")
{
this.Configuration.LazyLoadingEnabled = false;
this.Configuration.ProxyCreationEnabled = true;
}

public DbSet<Models.Game> Games { get; set; }

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
//Configure domain classes using modelBuilder here

base.OnModelCreating(modelBuilder);

modelBuilder.Entity<Models.Devices>().HasKey(d => d.GameId);
modelBuilder.Entity<Models.Players>().HasKey(p => p.TeamId);
modelBuilder.Entity<Models.Teams>().HasKey(t => t.GameId);
modelBuilder.Entity<Models.Scenario>().HasKey(s => s.GameId);

modelBuilder.Entity<Models.Game>().HasOptional<Models.Teams>(g => g.Teams).WithRequired(t => t.Game);
modelBuilder.Entity<Models.Game>().HasOptional<Models.Scenario>(g => g.Scenario).WithRequired(s => s.Game);
modelBuilder.Entity<Models.Game>().HasOptional<Models.Devices>(g => g.Devices).WithRequired(d => d.Game);

}
}
public static class GameService
{
public static List<Models.Game> GetGames()
{
using (var gctx = new Contexts.GameContext())
{
return gctx.Games.ToList();
}
}

public static void InsertGame(Models.Game game)
{
using (var gctx = new Contexts.GameContext())
{
gctx.Games.Add(game);
gctx.SaveChanges();
}
}
}


I'm trying to use it all like this:

List<Models.Game> games = Services.GameService.GetGames().ToList();

foreach(var game in games)
{
Console.WriteLine("Game " + game.GameId);

foreach (var team in game.Teams)
{
Console.Write("\t");
Console.WriteLine("Team" + team.Number);
foreach(var player in team.Players)
{
Console.Write("\t\t");
Console.WriteLine("Player" + player.PlayerId);
}
}
}


When I run this code i see my games, teams for that games, but i can't reach players for each team. So my question is: what I'm doing wrong here?

Answer

OK, I resolved my problem. There were few reasons which caused the problem.

  1. Need to use Include for Eager Loading. Method looks like that:

    public static List<Models.Game> GetGames()
    {
        using (var gctx = new Contexts.DatabaseContext())
        {
    
            return gctx.Games.Include(g => g.Teams).Include(g => g.Teams.TeamsList.Select(t => t.Players)).ToList();
        }
    }
    
  2. I used Fluent API to determine relationships (overriding DatabaseContext.OnModelCreating):

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
    
        modelBuilder.Entity<Models.Game>().HasOptional(g => g.Teams).WithOptionalPrincipal(t => t.Game); // 1 -> 0..1
        modelBuilder.Entity<Models.Game>().HasOptional(g => g.Devices).WithOptionalPrincipal(d => d.Game); // 1 -> 0..1
        modelBuilder.Entity<Models.Game>().HasOptional(g => g.Scenario).WithOptionalPrincipal(s => s.Game); // 1-> 0..1
    
        modelBuilder.Entity<Models.Teams>().HasMany(ts => ts.TeamsList).WithRequired(t => t.Teams); // 1 -> many
        modelBuilder.Entity<Models.Team>().HasMany(t => t.Players).WithRequired(p => p.Team); // 1 -> many
    
        base.OnModelCreating(modelBuilder);
    
    
    }
    
  3. Only in Game class navigation properties are NOT virtual.

Thanks for any help in this case. You're wonderful, guys!

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