如何将行号投影到Linq查询结果

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

这是我的尝试：

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 ++”行会引发下面的编译时exception：

“expression式树可能不包含赋值运算符”

Answer 1

那么，最简​​单的方法是在客户端而不是数据库端执行，并使用Select提供的索引的重载：

 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

好的，那就是诀窍。 谢谢。

这是我最终的代码…

服务器：

 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>(); } } 

客户：

 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(); } 

Answer 3

您也可以对原始代码进行一些微调，以使其工作。 谨慎的话，如果你再次绑定或访问对象，秩会每次增加。 在这些情况下，最好的答案是更好的。

 let Rank = i++ 

和

 Rank.ToString() 

完整代码：

 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 let Rank = i++ where s.Game.Id == guid orderby s.PlayerScore descending select new ScoreWithRank() { Rank.ToString(), PlayerName = s.PlayerName, PlayerScore = s.PlayerScore }; return query.ToList<ScoreWithRank>(); } 

}

Answer 4

这个解决scheme为我工作。 http://www.dotnetfunda.com/articles/article1995-rownumber-simulation-in-linq.aspx

 .Select((x, index) => new { SequentialNumber = index + 1 ,FieldFoo = x.FieldFoo }).ToList();