How To Project a Line Number Into Linq Query Results

Question

How can I project the row number onto the linq query result set.

Instead of say:

field1, field2, field3

field1, field2, field3

I would like:

1, field1, field2, field3

2, field1, field2, field3

Here is my attempt at this:

public List<ScoreWithRank> GetHighScoresWithRank(string gameId, int count)
{
    Guid guid = new Guid(gameId);
    using (PPGEntities entities = new PPGEntities())
    {
        int i = 1;
        var query = from s in entities.Scores
                    where s.Game.Id == guid
                    orderby s.PlayerScore descending
                    select new ScoreWithRank()
                    {
                        Rank=i++,
                        PlayerName = s.PlayerName,
                        PlayerScore = s.PlayerScore
                    };
        return query.ToList<ScoreWithRank>();
    }
}

Unfortunately, the "Rank=i++" line throws the following compile-time exception:

"An expression tree may not contain an assignment operator"

Answer 1

Well, the easiest way would be to do it at the client side rather than the database side, and use the overload of Select which provides an index as well:

public List<ScoreWithRank> GetHighScoresWithRank(string gameId, int count)
{
    Guid guid = new Guid(gameId);
    using (PPGEntities entities = new PPGEntities())
    {
        var query = from s in entities.Scores
                    where s.Game.Id == guid
                    orderby s.PlayerScore descending
                    select new
                    {
                        PlayerName = s.PlayerName,
                        PlayerScore = s.PlayerScore
                    };

        return query.AsEnumerable() // Client-side from here on
                    .Select((player, index) => new ScoreWithRank()
                            {
                                PlayerName = player.PlayerName,
                                PlayerScore = player.PlayerScore,
                                Rank = index + 1;
                            }
                    .ToList();

    }
}

Answer 2

Ok, that did the trick. Thanks.

Here is my final code...

Server:

public List<Score> GetHighScores(string gameId, int count)
{
    Guid guid = new Guid(gameId);
    using (PPGEntities entities = new PPGEntities())
    {
        var query = from s in entities.Scores
                    where s.Game.Id == guid
                    orderby s.PlayerScore descending
                    select s;
        return query.ToList<Score>();
    }                                                                      
}

Client:

void hsc_LoadHighScoreCompleted(object sender, GetHighScoreCompletedEventArgs e)
{
    ObservableCollection<Score> list = e.Result;

    _listBox.ItemsSource = list.Select((player, index) => new ScoreWithRank()
                            {
                                PlayerName = player.PlayerName,
                                PlayerScore = player.PlayerScore,
                                Rank = index+=1
                            }).ToList();
}