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" );