34

如何将行号投影到 linq 查询结果集。

而不是说：

场 1、场 2、场 3

场 1、场 2、场 3

我想：

1、字段1、字段2、字段3

2、字段1、字段2、字段3

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++”行抛出以下编译时异常：

“表达式树可能不包含赋值运算符”

4

5 回答 5

55

好吧，最简单的方法是在客户端而不是数据库端执行此操作，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();

    }
}
于 2008-12-13T11:39:31.277 回答
1

好的，这成功了。谢谢。

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：

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();
}
于 2008-12-13T12:09:37.957 回答
0

您也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该对象，Rank 将每次递增。在这些情况下，最佳答案更好。

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>();
}

}

于 2012-02-03T18:39:37.267 回答
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();
于 2013-02-03T12:56:14.120 回答
0 
List<Emp> Lstemp = GetEmpList(); 
int Srno = 0; 
var columns = from t in Lstemp 
              orderby t.Name 
              select new { 
                  Row_number=++Srno, 
                  EmpID = t.ID, 
                  Name = t.Name, 
                  City = t.City 
              };
于 2019-01-12T14:48:34.290 回答