Can't seem to get OneToMany relation working

Question

I'm very new to Mobile App Development so i'm trying to teach myself. I'm using Xamarin and sqlite-net (extensions) for this particular app i'm trying to make.

I have 2 classes with a OneToMany relationship

class Game
{
    [PrimaryKey, AutoIncrement]
    public int Id { get; set; }
    public string Name { get; set; }

    [OneToMany(CascadeOperations = CascadeOperation.All)]
    public List<Player> Players { get; set; }

    public Game()
    {
        Players = new List<Player>();
    }
}

class Player
{
    [PrimaryKey, AutoIncrement]
    public int Id { get; set; }
    [MaxLength(8)]
    public string Name { get; set; }

    [ForeignKey(typeof(Game))]
    public int GameId { get; set; }

    [ManyToOne]
    public Game Game { get; set; }

}

Now in my activity I have something like this

        SQLiteConnection db = new SQLiteConnection(new SQLite.Net.Platform.XamarinAndroid.SQLitePlatformAndroid(), path);

        db.CreateTable<Player>(); 
        db.CreateTable<Game>();

        Game game = new Game();
        game.Name = "Stupid game";

        Game game2 = new Game();
        game2.Name = "Fun game";

        Game game3 = new Game(); 
        game3.Name =  "Amazing game";

        db.Insert(game);
        db.Insert(game2);
        db.Insert(game3);

        Player player = new Player();
        player.Name = name; //Getting this from a input field
        db.Insert(player);

        Random random = new Random();                     
        player.GameId = random.Next(1, 3);
        Game game = db.Get<Game>(player.GameId);
        player.Game = game;

        db.UpdateWithChildren(player);

        game.Players.Add(player);
        db.UpdateWithChildren(game);

This all seems to work and gives me no errors. When I debug this I can see that the player is indeed added with a Game. However when I try somewhere else to get all the players using the following statement,

 List<Player> players = db.Table<Player>().ToList();

they suddenly don't have a Game anymore and my program crashes when I try to read that property.

I've tried a few different things with the UpdateWithChildren and InsertWithChildren but to no avail. Is there something I'm doing wrong or is it something I haven't installed or? I really appreciate the help.

I believe there is a recursive second parameter in the `UpdateWithChildren` that might be needed. If not there, you would have to do it in your `read` method via `conn.GetWithChildren(identifier, recursive: true);` — Jon Douglas, Nov 28 '16 at 21:04

score 0 · Answer 1 · answered Nov 29 '16 at 15:49

The thing about sqlite-net extensions is that you cannot go "Back" to using regular sqlite-net methods if you want to obtain children relationships. Thus you will have to follow their documentation here:

https://bitbucket.org/twincoders/sqlite-net-extensions

They provide methods such as GetChildren, UpdateWithChildren, etc in which you will have to use over the generic db.Table<T> methods.

If you decide to use the recursive methods, be sure to provide the optional recursive parameter.

Thus you should be able to do something along the lines of:

conn.GetWithChildren<Player>(identifier, recursive: true)

Otherwise read up more on the Cascade Operations section of the documentation linked above.

Can't seem to get OneToMany relation working

1 Answers1