事件的重现(LINQ查询)

Question

我有DateStart，DateEnd Periodicity，TypePeriodicity字段。

我们有一个问题：

var result = Events.Where(e => e.DateStart <=today && e.DateEnd >= today).ToList();

我希望这个查询检查Periodicity。

例如：

name  - record1
DateStart = 2012-02-02
DateEnd = 2012-03-31
Periodicity = 2
TypePeriodicity = 1 ( it's mean a week, may be also day = 0, month=2): 

我想要以下内容，如果当前日期等于：

2,3,4,5 February - return `record1`   
6,7,8..12 - not return, because TypePeriodicity = 1 and Periodicity = 2, which means every 2 weeks
13..19 - return `record1`
20..26 - not return  
and so on until `DateEnd`

谢谢。

PS。也许不是LINQ，而是接收result作为参数的简单方法。

Answer 1

这里有一些东西可以让你入门：

您可以像这样定义一个DateEvaluator委托：

    delegate bool DateEvaluator(DateTime startDate, DateTime endDate, DateTime dateToCheck, int periodicity);

委托的目的是评估给定周期类型的日期是否应被视为在范围内。因此，我们将有3个日期计算器。每种周期类型一个:让我们称它们为dayPeriodicityChecker、weekPeriodicityChecker和monthPeriodicityChecker

我们的dayPeriodicityChecker很简单：

        DateEvaluator dayPeriodicityChecker = (startDate, endDate, dateToCheck, periodicity) =>
            {
                if ((dateToCheck < startDate) || (dateToCheck > endDate))
                    return false;

                TimeSpan dateDiff = dateToCheck - startDate;
                return dateDiff.Days % periodicity == 0;
            };

我们的weekPeriodicityChecker需要考虑周的开始日期，因此需要将开始日期调整为startDate周实际开始的日期：

        DateEvaluator weekPeriodicityChecker = (startDate, endDate, dateToCheck, periodicity) =>
            {
                if ((dateToCheck < startDate) || (dateToCheck > endDate))
                    return false;

                DateTime adjustedStartDate = startDate.AddDays(-(int)startDate.DayOfWeek + 1);
                TimeSpan dateDiff = dateToCheck - adjustedStartDate;
                return (dateDiff.Days / 7) % periodicity == 0;
            };

我们的monthPeriodicityChecker需要用可变的天数满足几个月的需求：

        DateEvaluator monthPeriodicityChecker dateToCheck, periodicity) =>
            {
                if ((dateToCheck < startDate) || (dateToCheck > endDate))
                    return false;

                int monthDiff = 0; 
                while (startDate.AddMonths(1) < dateToCheck)
                {
                    monthDiff++
                    // i'm sure there is a speedier way to calculate the month difference, but this should do for the purpose of this example 
                }

                return (monthDiff - 1) % periodicity == 0;
            };

一旦你定义了所有的日期赋值器，你就可以将它们放在一个数组中，如下所示：

        DateEvaluator[] dateEvaluators = new DateEvaluator[] 
        {
            dayPeriodicityChecker,
            weekPeriodicityChecker,
            monthPeriodicityChecker
        };

这将允许您执行以下操作：

int periodicityType = 0; // or 1=week or 2=months
bool isDateIn = dateEvaluators[periodicityType ](startDate, endDate, dateTocheck, Periodicity)

因此，让我们来测试一下：

        PeriodicityEvent pEvent = new PeriodicityEvent
        {
            Name = "record1",
            DateStart = new DateTime(2012, 02, 02),
            DateEnd = new DateTime(2012, 03, 31),
            PeriodicityType = 1,
            Periodicity = 2
        };

        DateTime baseDate = new DateTime(2012, 02, 01);
        for (int i = 0; i < 30; i++)
    {
            DateTime testDate = baseDate.AddDays(i);
            if (dateEvaluators[pEvent.PeriodicityType](pEvent.DateStart, pEvent.DateEnd, testDate, pEvent.Periodicity))
            {
                Console.WriteLine("{0} is in", testDate.ToString("dd MMM"));
            }
            else
            {
                Console.WriteLine("{0} is out", testDate.ToString("dd MMM"));
            }
   }

这将产生所需的输出，如下所示：

​

​

要使用您，只需执行以下操作：

Events.Where(e => dateEvaluators[e.PeriodType](e.DateStart, e.DateEnd, today, e.Periodicity).ToList();

祝好运!