查找最小日期时间并将日期时间分配给本地变量

本文关键字：时间 日期 变量 分配 查找 | 更新日期: 2023-09-27 18:00:28

我试图获得最小日期时间，然后是最大日期时间，并将两者进行比较。但是，当我尝试从LINQ中提取DateTime值时，会出现以下错误。任何帮助都将不胜感激。

此行引发错误：appChartDateStart=Convert.ToDateTime（dateStartType）；

Allan

无法强制转换类型为"WhereSelectEnumerableIterator 2[System.Linq.IGrouping 2[System.DateTime，LatencyApp.Domain.Models.ChartHist]，<>"的对象f_AnonymousType2"1[System.DateTime]]"类型为"System.IConvertable"。

我的代码：

        DateTime appChartDateStart = DateTime.MinValue;
        DateTime appChartDateEnd = DateTime.MinValue;
        var dateStartType = from row in myRow
                                group row by row.LoginDateTime_Rounded into g
                                select new { MinDateTime = g.Min(row => row.LoginDateTime_Rounded) };
        var dateEndType = from row in myRow
                                group row by row.LoginDateTime_Rounded into g
                                select new { MinDateTime = g.Max(row => row.LoginDateTime_Rounded) };
        appChartDateStart = Convert.ToDateTime(dateStartType);
        appChartDateEnd = Convert.ToDateTime(dateEndType);
        TimeSpan difAppChart = appChartDateEnd - appChartDateStart;

查找最小日期时间并将日期时间分配给本地变量

我在LINQ sintax中做过，它运行得很好，也有点干净：

DateTime appChartDateStart = DateTime.MinValue;
DateTime appChartDateEnd = DateTime.MinValue;
var dateStartType = myRow.GroupBy(x => x.LoginDateTime_Rounded).Select(x => x.Key).Min();
var dateEndType = myRow.GroupBy(x => x.LoginDateTime_Rounded).Select(x => x.Key).Max();
TimeSpan difAppChart = appChartDateEnd - appChartDateStart;

完成代码：

        DateTime appChartDateStart = DateTime.MinValue;
        DateTime appChartDateEnd = DateTime.MinValue;
        if (histByApp.Count() != 0)
        {
            var dateStartType = histByApp.GroupBy(x => x.LoginDateTime_Rounded).Select(x => x.Key).Min();
            var dateEndType = histByApp.GroupBy(x => x.LoginDateTime_Rounded).Select(x => x.Key).Max();
            appChartDateStart = Convert.ToDateTime(dateStartType);
            appChartDateEnd = Convert.ToDateTime(dateEndType);
        }
        TimeSpan difAppChart = appChartDateEnd - appChartDateStart;

这是因为您的选择正在创建一个具有属性MinDateTime的匿名类型。Convert.TomDateTime方法不知道如何转换此匿名类型。尝试做：

DateTime appChartDateStart = DateTime.MinValue;
DateTime appChartDateEnd = DateTime.MinValue;
var dateStartType = (from row in myRow
                        group row by row.LoginDateTime_Rounded into g
                        select new { MinDateTime = g.Min(row => row.LoginDateTime_Rounded) }).FirstOrDefault();
var dateEndType = (from row in myRow
                        group row by row.LoginDateTime_Rounded into g
                        select new { MinDateTime = g.Max(row => row.LoginDateTime_Rounded) }).FirstOrDefault();
appChartDateStart = Convert.ToDateTime(dateStartType);
appChartDateEnd = Convert.ToDateTime(dateEndType);
TimeSpan difAppChart = appChartDateEnd - appChartDateStart;
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