c# - 使用 LINQ 填充列表

Question

我有一个类型为 RawResults 的 ArrayList，其中 RawResults 是位置和日期

public class RawResult
{
    public string location { get; set; }
    public DateTime createDate {get; set; }

    public RawResults(string l, DateTime d)
    {
        this.location = l;
        this.createDate = d;
    }
}

我想使用 LINQ 填充一个列表，其中包含每个不同的位置以及它在我的数组列表中出现的次数。如果我能够在 SQL 中完成它，它看起来像这样

select 
   bw.location, 
   count(*) as Count
from 
   bandwidth bw, 
   media_log ml
where
   bw.IP_SUBNET = ml.SUBNET
   group by bw.location
   order by location asc

稍后我也必须做同样的事情，但在给定的日期范围内。

更新 这是为获取 rawData

中的所有数据而运行的查询

SELECT        
    MEDIASTREAM.BANDWIDTH.LOCATION, MEDIASTREAM.MEDIA_LOG.CREATE_DATE
FROM            
    MEDIASTREAM.BANDWIDTH INNER JOIN
      MEDIASTREAM.MEDIA_LOG ON MEDIASTREAM.BANDWIDTH.IP_SUBNET =     
      MEDIASTREAM.MEDIA_LOG.SUBNET

现在我需要查询 rawData 中返回的数据以获得不同的结果集。我有一个列表可供查询。

Answer 1

你可以这样做:

var results = 
    (from bw in data.bandwith
     join ml in data.media_log on bw.IP_SUBNET equals ml.SUBNET
     group bw by bw.location into g
     orderby g.Key
     select new 
     { 
         location = g.Key, 
         Count = g.Count() 
     })
    .ToList();

尽管 ToList没有必要，除非你绝对需要它是一个List<T> .要按时间过滤，您可以这样做:

var results = 
    (from bw in data.bandwith
     join ml in data.media_log on bw.IP_SUBNET equals ml.SUBNET
     where bw.createDate >= minDate && bw.createDate <= maxDate
     group bw by bw.location into g
     orderby g.Key
     select new 
     { 
         location = g.Key, 
         Count = g.Count() 
     })
    .ToList();

---

如果media_log不相关，您可以省略 join :

var results = 
    from bw in data.bandwith
    group bw by bw.location into g
    orderby g.Key
    select new 
    { 
        location = g.Key, 
        Count = g.Count() 
    }

或者用流利的语法:

var results = data.bandwith
    .GroupBy(bw => bw.location, (k, g) => new { location = k, Count = g.Count() })
    .OrderBy(r => r.location);

要按日期过滤，只需使用这个:

var results = 
    from bw in data.bandwith
    where bw.createDate >= minDate && bw.createDate <= maxDate
    group bw by bw.location into g
    orderby g.Key
    select new 
    { 
        location = g.Key, 
        Count = g.Count() 
    };

或者用流利的语法:

var results = data.bandwith
    .Where(bw => bw.createDate >= minDate && bw.createDate <= maxDate)
    .GroupBy(bw => bw.location, (k, g) => new { location = k, Count = g.Count() })
    .OrderBy(r => r.location);

注意，要使用 ArrayList ，或 Linq 查询中的任何其他非通用集合类型，请使用 Cast<T> 或 OfType<T> 方法，像这样:

var results = bandwithArrayList
    .Cast<RawResults>()
    .GroupBy(bw => bw.location, (k, g) => new { location = k, Count = g.Count() })
    .ToList();