C# 高效的LINQ到实体查询
我有一个C# 高效的LINQ到实体查询,c#,.net,linq,entity-framework,linq-to-entities,C#,.net,Linq,Entity Framework,Linq To Entities,我有一个读数的实体集合。 每个读数都链接到一个名为仪表的实体。 (并且每个仪表都有多个读数)。 每个读数都包含一个仪表id(int)字段和一个时间字段 下面是一些简化的代码来演示: public class Reading { int Id; int meterId; DateTime time; } public class Meter { int id; ICollection<Readings> readings; } 公共课
读数的实体集合
。
每个读数
都链接到一个名为仪表
的实体。
(并且每个仪表
都有多个读数)。
每个读数
都包含一个仪表id(int)字段和一个时间字段
下面是一些简化的代码来演示:
public class Reading
{
int Id;
int meterId;
DateTime time;
}
public class Meter
{
int id;
ICollection<Readings> readings;
}
公共课阅读
{
int-Id;
内特梅特里德;
日期时间;
}
公共类仪表
{
int-id;
i收集读数;
}
给定特定的时间段和meterid
s列表,
每米最有效的方式是什么
那个时期的第一次和最后一次阅读
我能够遍历所有米,并为每米遍历obatin
这一时期的第一次和最后一次阅读,
但我想知道是否有更有效的方法来实现这一点
还有一个奖金问题:同一个问题,但需要多个时段来获取数据,
而不仅仅是一个句点。我不确定您希望如何使用此数据,但您可以将其投影为匿名类型:
var metersFirstAndLastReading = meters.Select(m => new
{
Meter = m,
FirstReading = m.readings.OrderBy(r => r.time).First(),
LastReading = m.readings.OrderBy(r => r.time).Last()
});
然后,您可以像这样阅读结果列表(此示例仅用于说明):
另一个选项是在仪表中创建属性,动态返回第一个和最后一个读数:
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();
}
}
}
您现在将无法使用属性(因为您需要提供参数),因此方法可以作为替代方法正常工作:
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);
}
}
公共类仪表
{
公共int id;
公开阅读书目;
公共读取GetFirstReading(日期时间开始,日期时间结束)
{
var filteredrardings=reads.Where(r=>r.time>=begin&&r.time r.time).First();
}
公共读取GetLastReading(日期时间开始,日期时间结束)
{
var filteredrardings=读数。其中(r=>r.time>=开始和&r.time r.time).Last();
}
公共布尔值(日期时间开始,日期时间结束)
{
return reads.Any(r=>r.time>=begin&&r.time创建一个新类作为名为Result
的返回类型,如下所示
public class Result
{
public int MeterId;
public Readings Start;
public Readings Last;
}
我模拟了您的情况,制作了一个仪表列表并填充了一些数据,但是您的查询应该基本相同
var reads = Meters.Where(x => x.readings != null)
.Select(x => new Result
{
MeterId = x.id,
Start = x.readings.Select(readings => readings).OrderBy(readings=>readings.time).FirstOrDefault(),
Last = x.readings.Select(readings=>readings).OrderByDescending(readings=>readings.time).FirstOrDefault()
});
public IEnumerable GetFirstAndLastInPeriod
(IEnumerable reads,日期时间开始,日期时间结束)
{
返回
从阅读中学习
让span=读数。其中(item=>item.time>=begin&&item.time item.time)
||reading.time==span.Min(item=>item.time)
选择阅读;
}
meters.Where(mt=>desiredMeters.Contains(mt))。选择(mt=>
新的{
西德山,
First=mt.Readings.Where().OrderBy(rd=>rd.Time).FirstOrDefault(),
Last=mt.Readings.Where().OrderBy(rd=>rd.Time).LastOrDefault()
});
如果每米有大量的读数,这将不能很好地执行,并且你应该把读数看作是排序列表类。
< P>我的解决方案将精确地返回你想要的<强>(在给定时间段内包含所有读数的列表)< /强>
public IList GetFirstandLastReaders(列表meterList、DateTime start、DateTime end)
{
IList fAndlReadingsList=新列表();
meterList.ForEach(x=>x.Reads.ForEach(y=>
{
var readingList=新列表();
if(y.time>=startTime&&y.time reading.time).First(),readingList.OrderBy(reading=>reading.time.Last());
}
}));
返回FandReadingList;
}
我有一个非常相似的数据模型,其中该代码用于获取最旧的读数,我只是将其更改为包含最新的读数
我使用查询语法执行以下操作:
var query = from reading in db.Readings
group reading by reading.meterId
into readingsPerMeter
let oldestReadingPerMeter = readingsPerMeter.Min(g => g.time)
let newestReadingPerMeter = readingsPerMeter.Max(g => g.time)
from reading in readingsPerMeter
where reading.time == oldestReadingPerMeter || reading.time == newestReadingPerMeter
select reading; //returns IQueryable<Reading>
query.Where(r=>r.time > someTime1 && r.time < someTime2)
var query=从以db.reads为单位的读取
按reading.meterId分组阅读
读数渗透计
设oldestReadingPerMeter=readingpermeter.Min(g=>g.time)
设newestReadingPerMeter=readingpermeter.Max(g=>g.time)
从读数渗透计中读取
其中reading.time==旧的读取Permeter | | reading.time==新的读取Permeter
选择阅读//返回IQueryable
这将导致每一米的读数只有最新和最旧的读数
我认为这是有效的原因是,它只需一次对DB的查找,就可以得到每一个仪表的所有读数,而不是每一个仪表的几次查找。我们有大约40000米,读数为30英里。我刚刚对我们的数据进行了查找,大约用了10秒
预执行的sql是最小和最大日期的两个子选择之间的交叉连接
更新:
因为这是可查询的,所以您应该能够在之后提供一个句点,如下所示:
var query = from reading in db.Readings
group reading by reading.meterId
into readingsPerMeter
let oldestReadingPerMeter = readingsPerMeter.Min(g => g.time)
let newestReadingPerMeter = readingsPerMeter.Max(g => g.time)
from reading in readingsPerMeter
where reading.time == oldestReadingPerMeter || reading.time == newestReadingPerMeter
select reading; //returns IQueryable<Reading>
query.Where(r=>r.time > someTime1 && r.time < someTime2)
query.Where(r=>r.time>someTime1&&r.time
或者把它放到原来的查询中,我喜欢这样分开。查询尚未执行,因为我们尚未执行获取数据的操作。感谢所有响应者,我得到了一些非常好的线索。
以下是对我有效的解决方案:
/// <summary>
/// Fills the result data with meter readings matching the filters.
/// only take first and last reading for each meter in period.
/// </summary>
/// <param name="intervals">time intervals</param>
/// <param name="meterIds">list of meter ids.</param>
/// <param name="result">foreach meter id , a list of relevant meter readings</param>
private void AddFirstLastReadings(List<RangeFilter<DateTime>> intervals, List<int> meterIds, Dictionary<int, List<MeterReading>> result)
{
foreach (RangeFilter<DateTime> interval in intervals)
{
var metersFirstAndLastReading = m_context.Meter.Where(m => meterIds.Contains(m.Id)).Select(m => new
{
MeterId = m.Id,
FirstReading = m.MeterReading
.Where(r => r.TimeStampLocal >= interval.FromVal && r.TimeStampLocal < interval.ToVal)
.OrderBy(r => r.TimeStampLocal)
.FirstOrDefault(),
LastReading = m.MeterReading
.Where(r => r.TimeStampLocal >= interval.FromVal && r.TimeStampLocal < interval.ToVal)
.OrderByDescending(r => r.TimeStampLocal)
.FirstOrDefault()
});
foreach (var firstLast in metersFirstAndLastReading)
{
MeterReading firstReading = firstLast.FirstReading;
MeterReading lastReading = firstLast.LastReading;
if (firstReading != null)
{
result[firstLast.MeterId].Add(firstReading);
}
if (lastReading != null && lastReading != firstReading)
{
result[firstLast.MeterId].Add(lastReading);
}
}
}
}
}
//
///用与过滤器匹配的仪表读数填充结果数据。
///仅读取周期内每米的第一个和最后一个读数。
///
///时间间隔
///仪表ID列表。
///对于每个仪表id,相关仪表读数的列表
私有void addFirstLastReaders(列出间隔、列出米数、字典结果)
{
foreach(以间隔为单位的范围过滤器间隔)
{
var metersfirstandlastreating=m_context.Meter.Where(m=>meterIds.Contains(m.Id))。选择(m=>new
{
MeterId=m.Id,
第一次读数=米读数
.Where(r=>r.TimeStampLocal>=interval.FromVal&&r.TimeStampLocalr.Time
var query = from reading in db.Readings
group reading by reading.meterId
into readingsPerMeter
let oldestReadingPerMeter = readingsPerMeter.Min(g => g.time)
let newestReadingPerMeter = readingsPerMeter.Max(g => g.time)
from reading in readingsPerMeter
where reading.time == oldestReadingPerMeter || reading.time == newestReadingPerMeter
select reading; //returns IQueryable<Reading>
query.Where(r=>r.time > someTime1 && r.time < someTime2)
/// <summary>
/// Fills the result data with meter readings matching the filters.
/// only take first and last reading for each meter in period.
/// </summary>
/// <param name="intervals">time intervals</param>
/// <param name="meterIds">list of meter ids.</param>
/// <param name="result">foreach meter id , a list of relevant meter readings</param>
private void AddFirstLastReadings(List<RangeFilter<DateTime>> intervals, List<int> meterIds, Dictionary<int, List<MeterReading>> result)
{
foreach (RangeFilter<DateTime> interval in intervals)
{
var metersFirstAndLastReading = m_context.Meter.Where(m => meterIds.Contains(m.Id)).Select(m => new
{
MeterId = m.Id,
FirstReading = m.MeterReading
.Where(r => r.TimeStampLocal >= interval.FromVal && r.TimeStampLocal < interval.ToVal)
.OrderBy(r => r.TimeStampLocal)
.FirstOrDefault(),
LastReading = m.MeterReading
.Where(r => r.TimeStampLocal >= interval.FromVal && r.TimeStampLocal < interval.ToVal)
.OrderByDescending(r => r.TimeStampLocal)
.FirstOrDefault()
});
foreach (var firstLast in metersFirstAndLastReading)
{
MeterReading firstReading = firstLast.FirstReading;
MeterReading lastReading = firstLast.LastReading;
if (firstReading != null)
{
result[firstLast.MeterId].Add(firstReading);
}
if (lastReading != null && lastReading != firstReading)
{
result[firstLast.MeterId].Add(lastReading);
}
}
}
}
}