如何将行号投射到Linq查询结果中

Question

如何将行号投影到linq查询结果集上.

而不是说:

field1,field2,field3

field1,field2,field3

我想要:

1,field1,field2,field3

2,field1,field2,field3

以下是我对此的尝试:

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>();
    }
}

不幸的是,"Rank = i ++"行引发了以下编译时异常:

"表达式树可能不包含赋值运算符"

Answer 1

嗯,最简单的方法是在客户端而不是数据库端执行它,并使用Select的重载,它也提供索引:

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();

    }
}