13.01.17 C# Linq 查询最新的记录

var wcs = ( from wc in db.WorkConditions
where wc.RTU_ID == e.CoverdItem.PointName
orderby wc.time descending
select (wc)).AsEnumerable().First();

var wr1 = (from wr in db.WaterRatios
where wr.RTU_ID == e.CoverdItem.PointName & wr.Ch==1
orderby wr.time
select (wr.WR)).AsEnumerable().Last();
var wr2 = (from wr in db.WaterRatios
where wr.RTU_ID == e.CoverdItem.PointName & wr.Ch == 2
orderby wr.time
select (wr.WR)).AsEnumerable().Last();

mapControl1.ShowToolTip(e.CoverdItem.PointName, ""+
"土壤含水率1：" + (wr1 / 10.0).ToString() + "%\r\n" +
"土壤含水率2：" + (wr2 / 10.0).ToString() + "%\r\n" +
"电压："+(wcs.Voltage/10.0).ToString() +"V\r\n" +
"温度："+wcs.Temperature.ToString() +"℃\r\n" +
"GPRS信号强度："+wcs.si_0.ToString() +"\r\n" );

注意：

var wcs = ( from wc in db.WorkConditions

where wc.RTU_ID == e.CoverdItem.PointName

orderby wc.time descending

select (wc)).AsEnumerable().First();

var wr1 = (from wr in db.WaterRatios

where wr.RTU_ID == e.CoverdItem.PointName & wr.Ch==1

orderby wr.time

select (wr.WR)).AsEnumerable().Last();

var wr2 = (from wr in db.WaterRatios

where wr.RTU_ID == e.CoverdItem.PointName & wr.Ch == 2

orderby wr.time

select (wr.WR)).AsEnumerable().Last();

mapControl1.ShowToolTip(e.CoverdItem.PointName, ""+

"土壤含水率1：" + (wr1 / 10.0).ToString() + "%\r\n" +

"土壤含水率2：" + (wr2 / 10.0).ToString() + "%\r\n" +

"电压："+(wcs.Voltage/10.0).ToString() +"V\r\n" +

"温度："+wcs.Temperature.ToString() +"℃\r\n" +

"GPRS信号强度："+wcs.si_0.ToString() +"\r\n" );