如何将行号投射到Linq查询结果中

时间:2008-12-13 10:38:52

标签: linq row-number

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:

1,field1,field2,field3

2,field1,field2,field3

以下是我的尝试:

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 ++”行引发了以下编译时异常:

“表达式树可能不包含赋值运算符”

5 个答案:

答案 0 :(得分:55)

嗯,最简单的方法是在客户端而不是数据库端进行,并使用Select的重载来提供索引:

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();

    }
}

答案 1 :(得分:1)

好的,这就是诀窍。感谢。

这是我的最终代码......

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>();
    }                                                                      
}

客户端:

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();
}

答案 2 :(得分:0)

列表  Lstemp = GetEmpList(); int Srno = 0; var列=以Lstemp顺序中的t从t开始。名称选择新的{Row_number = ++ Srno,EmpID = t.ID,名称= t.Name,城市= t.City};

答案 3 :(得分:0)

这个解决方案对我有用。 http://www.dotnetfunda.com/articles/article1995-rownumber-simulation-in-linq.aspx

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

答案 4 :(得分:0)

您还可以对原始代码稍作调整,以使其正常工作。请注意,如果您再次数据绑定或访问对象,Rank将每次递增。在这些情况下,最佳答案是更好的。

let Rank = i++

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>();
}

}