我不确定您想要这些数据的具体形式,但您可以将其投影到一个匿名类型中:
var metersFirstAndLastReading = meters.Select(m => new
{
Meter = m,
FirstReading = m.readings.OrderBy(r => r.time).First(),
LastReading = m.readings.OrderBy(r => r.time).Last()
});
你可以像这样读取你的结果列表(这个例子只是为了说明):
foreach(var currentReading in metersFirstAndLastReading)
{
string printReadings = String.Format("Meter id {0}, First = {1}, Last = {2}",
currentReading.Meter.id.ToString(),
currentReading.FirstReading.time.ToString(),
currentReading.LastReading.time.ToString());
}
另一种选择是在Meter中创建属性,动态返回第一个和最后一个读数值:
public class Meter
{
public int id;
public List<Reading> readings;
public Reading FirstReading
{
get
{
return readings.OrderBy(r => r.time).First();
}
}
public Reading LastReading
{
get
{
return readings.OrderBy(r => r.time).Last();
}
}
}
编辑:我对问题的理解有些误解。
以下是实现来确定仪表的第一个和最后一个读数,包括日期范围(假设meterIdList
是ID的ICollection<int>
,而begin
和end
是指定的日期范围)。
var metersFirstAndLastReading = meters
.Where(m => meterIdList.Contains(m.id))
.Select(m => new
{
Meter = m,
FirstReading = m.readings
.Where(r => r.time >= begin && r.time <= end)
.OrderBy(r => r.time)
.FirstOrDefault(),
LastReading = m.readings
.Where(r => r.time >= begin && r.time <= end)
.OrderByDescending(r => r.time)
.FirstOrDefault()
});
现在您将无法使用属性(因为您需要提供参数),因此方法作为替代方案可以正常工作:
public class Meter
{
public int id;
public List<Reading> readings;
public Reading GetFirstReading(DateTime begin, DateTime end)
{
var filteredReadings = readings.Where(r => r.time >= begin && r.time <= end);
if(!HasReadings(begin, end))
{
throw new ArgumentOutOfRangeException("No readings available during this period");
}
return filteredReadings.OrderBy(r => r.time).First();
}
public Reading GetLastReading(DateTime begin, DateTime end)
{
var filteredReadings = readings.Where(r => r.time >= begin && r.time <= end);
if(!HasReadings(begin, end))
{
throw new ArgumentOutOfRangeException("No readings available during this period");
}
return filteredReadings.OrderBy(r => r.time).Last();
}
public bool HasReadings(DateTime begin, DateTime end)
{
return readings.Any(r => r.time >= begin && r.time <= end);
}
}
Queryable.First()
和Queryable.Last()
吗? - user1914530