Question

我有一个Status对象列表，其中包含int值和datetime，格式为

Tue Sep 30 21:22:02 +0000 2014

代码：

public class Status
{
    public string created_at { get; set; }

    public int value { get; set; }
}

现在，我想在图表上显示此信息，但仅限过去7天。

如何在C＃中按日期对对象进行分组并设法获取此信息？我知道如何在SQL中做到这一点，但我不熟悉LINQ。

Answer 1

我猜你需要将Status分组来计算或计算你班上的其他一些字段，这样你就可以在白天得到一些东西。

如果是，请给出以下示例

        List<Status> statusList = new List<Status>();
        statusList.Add(new Status() { Value = 12, CreatedAt = "Tue Sep 30 21:22:02 +0000 2014" });
        statusList.Add(new Status() { Value = 11, CreatedAt = "Tue Sep 30 21:22:02 +0000 2014" });
        statusList.Add(new Status() { Value = 10, CreatedAt = "Tue Sep 30 21:22:02 +0000 2014" });
        statusList.Add(new Status() { Value = 9, CreatedAt = "Sat Sep 27 21:22:02 +0000 2014" });
        statusList.Add(new Status() { Value = 8, CreatedAt = "Fri Sep 26 21:22:02 +0000 2014" });
        statusList.Add(new Status() { Value = 7, CreatedAt = "Thu Sep 25 21:22:02 +0000 2014" });
        statusList.Add(new Status() { Value = 6, CreatedAt = "Wed Sep 24 21:22:02 +0000 2014" });
        statusList.Add(new Status() { Value = 5, CreatedAt = "Tue Sep 23 21:22:02 +0000 2014" });
        statusList.Add(new Status() { Value = 4, CreatedAt = "Mon Sep 22 21:22:02 +0000 2014" });
        statusList.Add(new Status() { Value = 3, CreatedAt = "Sun Sep 21 21:22:02 +0000 2014" });
        statusList.Add(new Status() { Value = 2, CreatedAt = "Sat Sep 20 21:22:02 +0000 2014" });
        statusList.Add(new Status() { Value = 1, CreatedAt = "Fri Sep 19 21:22:02 +0000 2014" });



        var groups = from status in statusList
                  let date = DateTime.ParseExact(status.CreatedAt, "ddd MMM dd HH:mm:ss zzz yyyy", CultureInfo.InvariantCulture)
                  group status by date into g
                  where g.Key.Date >= DateTime.Now - new TimeSpan(7, 0, 0, 0)
                  select g;

        foreach (IGrouping<DateTime, Status> group in groups)
        {
            DateTime day = group.Key;
            int countOfValues = group.Select(g => g.Value).Count();
            Console.WriteLine("Day: {0}", day.ToString());
            Console.WriteLine("countOfValues: {0}", countOfValues.ToString());
        }

打印：

Day: 9/30/2014 4:22:02 PM
countOfValues: 3 //Three entries on Sep 30...
Day: 9/27/2014 4:22:02 PM
countOfValues: 1
Day: 9/26/2014 4:22:02 PM
countOfValues: 1
Day: 9/25/2014 4:22:02 PM
countOfValues: 1
Day: 9/24/2014 4:22:02 PM
countOfValues: 1

Answer 2

尝试添加以下内容，然后您的SP / SQL查询将在7天内仅返回记录。

datediff(day, created_at, getdate()) < 7

Answer 3

如果您使用的是int（它非常糟糕，但确定..）那么首先您必须将int转换为datetime：在Google int to datetime上搜索。

实施TimeSpan的第二步，并为Datetime和TimeSpan使用覆盖运算符。

public bool LaterThan7Days(int valueFromClass)
{
    DateTime myTime = //here convert valueFromClass to Datetime, search in google please
    TimeSpan t = new TimeSpan(7,0 , 0, 0); //days, hours ,mins, seconds
    DateTime timeToCompare = myTime + t;
    return timeToCompare > DateTime.Now;
}

，查询应如下所示：

var query = from Status in yourContext
            where LaterThan7Days(Status.value)
            select Status;

query.ToList().Foreach(p=> Console.WriteLine(p.created_at));

为列表查询分组和设置条件

3 个答案: