Question

我有一个自定义列表，如下所示。

class ActionToDo
{
    public string Name {get;set;}
    public DateTime dtDate {get;set;}
    public string EventCode {get;set;}
    public string EventDescription {get;set;}
}

我想做的是查找具有相同日期和日期的项目。相同的事件描述以及EventCode = "AQ"的位置。我猜LINQ是达到这个目标的最好方法吗？虽然使用LINQ，但我不知道如何做到这一点。

在我的头脑中使用Sql我认为它大致类似于下面的内容。

SELECT * FROM SomeTable
WHERE [EventDescription] = 'AQ'
GROUP BY [dtDate], [EventDescription]

Answer 1

.Where(x=> x.EventDescription == "AQ")
.GroupBy(x => new { x.dtDate.Date, x.EventDescription})

Answer 2

所以我们假设你有一个

List<ActionToDo> actionToDo = new List<ActionToDo>();
actionToDo.Where(i => i.EventDescription == "AQ" && i.EventCode="AQ")
.GroupBy(i => new { i.dtDate.Date, i.EventDescription });

Answer 3

以下是使用符合您要求的查询语法表达的LINQ查询。此外，它还会对分组属性dtDate和EventDescription进行排序，然后按Name对每个组的成员进行排序：

var actions = new List<ActionToDo>();
// populate 'actions'

var results =
    from a in actions
    where a.EventCode == "AQ"
    orderby a.dtDate, a.EventDescription, a.Name
    group a by new { a.dtDate, a.EventDescription };

为了演示此查询，我以随机顺序创建了一个包含一些样本ActionToDo数据的程序。请参阅下面的程序格式化输出，然后是程序本身。

演示程序输出

[2014-02-12] [Desc.AQ.12]
  AQ.12a
  AQ.12b
[2014-02-13] [Desc.AQ.13]
  AQ.13a
  AQ.13b
  AQ.13c
[2014-02-14] [Desc.AQ.14]
  AQ.14a
  AQ.14b

演示计划

using System;
using System.Collections.Generic;
using System.Linq;

class GroupByDemo
{
    static public void Main(string[] args)
    {
        var actions = new List<ActionToDo>()
            {
                new ActionToDo("AQ.14b", "2014-02-14", "AQ", "Desc.AQ.14"),
                new ActionToDo("AQ.12a", "2014-02-12", "AQ", "Desc.AQ.12"),
                new ActionToDo("AQ.13b", "2014-02-13", "AQ", "Desc.AQ.13"),
                new ActionToDo("XX.01",  "2014-02-01", "XX", "Desc.XX.01"),
                new ActionToDo("AQ.14a", "2014-02-14", "AQ", "Desc.AQ.14"),
                new ActionToDo("AQ.12b", "2014-02-12", "AQ", "Desc.AQ.12"),
                new ActionToDo("AQ.13a", "2014-02-13", "AQ", "Desc.AQ.13"),
                new ActionToDo("XX.02",  "2014-02-02", "XX", "Desc.XX.02"),
                new ActionToDo("AQ.13c", "2014-02-13", "AQ", "Desc.AQ.13"),
                new ActionToDo("XX.03",  "2014-02-03", "XX", "Desc.XX.03")
            };

        var results =
            from a in actions
            where a.EventCode == "AQ"
            orderby a.dtDate, a.EventDescription, a.Name
            group a by new { a.dtDate, a.EventDescription };

        foreach (var group in results)
        {
            Console.WriteLine("[{0}] [{1}]",
                              group.Key.dtDate.ToString("yyyy-MM-dd"),
                              group.Key.EventDescription);

            foreach (var action in group)
            {
                Console.WriteLine("  {0}", action.Name);
            }
        }
    }
}

class ActionToDo
{
    public string Name {get;set;}
    public DateTime dtDate {get;set;}
    public string EventCode {get;set;}
    public string EventDescription {get;set;}

    public ActionToDo(
        string name,
        string dtDateString,
        string eventCode,
        string eventDescription)
    {
        this.Name = name;
        this.dtDate = DateTime.Parse(dtDateString);
        this.EventCode = eventCode;
        this.EventDescription = eventDescription;
    }
}

C＃Linq Groupby和Where

3 个答案: