.net - 将两个LINQ查询合并为一个

我的表有大约15个不同的字段，其中一些是JobID(整数字段)，Cost(整数字段)和LastUpdated(DateTime字段)

JobID  Cost      LastUpdated
 1      10        10-July-2011
 1      15        11-June-2011
 2      25        5-May-2011
 1      15        12-April-2011

Is it possible to write one LINQ query to get the sum of Cost for job id = 1 and also the last date such a cost incurred?

The example query output for the sample data above to look like this below:

40 , 10-july-2011

Currently I am doing it with two different linq queries like this, resulting in two hits to the database from the website in this particular case.

//for last updated
(from row in MyTable where row.JobID == 1
 orderby row.LastUpdated descending
 select row.LastUpdated).First()

//for sum of cost
(from row in MyTable
 where row.JobID == 1
 select row.Cost).Sum()

在这种情况下，一个linq查询会更好吗？在整个页面加载期间，类似的情况将导致对数据库的多次命中，总共9次访问9个不同的表。通过在一个查询中组合总和和LastUpdated日期，我试图将该命中数减少到9，每个表一个。

谢谢你的时间...

最佳答案

是的，您可以像这样执行group by

var query = from row in MyTable
            group row by row.JobID into rows
            where rows.Key == 1
            select new
            {
              LastUpdated = rows.Select(x => x.LastUpdated).OrderByDescending(x => x).First(),
              Cost = rows.Sum(x => x.Cost),
            };