MongoDB C#Driver resp. Linq: query for unique instances and using static AsQueryable Properties

Question

I am working on a rather large MongoDB database and am wondering if there is a more effective way to some queries. For example, I store lots of instances of Game in the db, where the Game class looks as follows:

public class Game{
    [BsonId]
    public long ID { get; set; }

    // ... some more properties

    public List<Player> Players { get; set; }
}

where each game instance has a list of Player , which in turn has some properties, like Name .

In one view model I want to bind a ComboBox to the name of all players in the database - but recall that the same player might have played many games. I load them as follows:

private void LoadPlayersNames() {
    var _l = StaticMongo.GetGames.SelectMany(n => n.Players).Select(n => n.Name);
    PlayerNames = new ObservableCollection<string>(new HashSet<string>(_l));
}

And in the static class StaticMongo I have a static instance of the MongoClient and the IMongoDatabase , And I expose the GetGames property in StaticMongo as follows,

private readonly static IMongoDatabase _database;
public static IMongoQueryable<DetailedHand> GetGames { 
    get {
        return _database.GetCollection<Game>("Games").AsQueryable();
    } 
}

So to make this more conrete, following questions:

1: Is the way I get the unique player names (via HashSet ) a good way or is there a better way to query for unique names in this context. 2: Does the static MongoDB instance, together with exposing the database collections AsQueryable have drawbacks?

I know the formulaion might be a bit opinion-based, yet I hope to get some alternative ways to do queries of this kind as this does not look to be the ideal way to me.

Answer 1

I feel you should use aggregation framework for finding unique names which is faster:

Pure mongo query would be:

db.games.aggregate( 
     { 
        "$unwind": "$players"   
     },   
     { 
        "$group": { 
            "_id": "$players.name",             
        }  
    }
 )

You can see MongoDB Aggregation Framework Examples in C# for converting my db query to C# usage.

Update:

Learning aggregation in C# for you. Believe me or not. But aggregation is faster than AsQueryable()

var collection = _database.GetCollection<BsonDocument>("games");
var pipeline = collection.Aggregate()
    .Unwind(i => i.players)
    .Group(new BsonDocument { { "_id", "$players.name" } });

Check if it is working.