我试图创建一个LINQ查询,这将产生相同的结果,因为这SQL实例:LINQ GROUP BY /选择 - 对象引用不设置到对象
SELECT Priority.PriorityKey, Count(Priority.PriorityKey) AS NewPresentingUnits
FROM Priority INNER JOIN SupportPeriod ON Priority.PriorityCode = SupportPeriod.PriorityCode
WHERE (((SupportPeriod.NewClient)=True) AND ((SupportPeriod.DateAssistanceRequested) Between #1/1/2013# And #2/1/2013#) AND ((SupportPeriod.DateFinished) Between #1/1/9999# And #12/31/9999#))
GROUP BY Priority.PriorityKey;
我得到以下结果当我运行SQL查询:
https://docs.google.com/file/d/0B6b_N7sDgjmvRlBtT1lZWURERVU/edit?usp=sharing
这是LINQ声明:
SupportPeriodTableAdapter spTa = new SupportPeriodTableAdapter();
SupportPeriodDataTable dataTables = spTa.GetData();
var test = (from sp in dataTables
where (sp.NewClient == true) &&
(sp.DateAssistanceRequested >= new DateTime(2013, 1, 1) &&
sp.DateAssistanceRequested <= new DateTime(2013, 2, 1)) &&
(sp.DateFinished > new DateTime(2013, 2, 1))
group sp by sp.PriorityRow.PriorityKey into groupz
select new { Key = groupz.Key, sount = groupz.Count() });
当我尝试调试var test
时,我在结果视图中将“对象引用未设置为对象的实例”。
https://docs.google.com/file/d/0B6b_N7sDgjmvdGp0bjJCNkE3TTg/edit?usp=sharing
我是新来使用“GROUP BY”和“选择新的” LINQ的功能,因此我有一个很难搞清楚了这一点....
'sp.PriorityRow'可能是罪魁祸首 – NSGaga 2013-04-08 01:15:24
@NSGaga SupportPeriod表中的所有FK在Priority表中都有一个有效的PK ...你的意思是我应该使用多个查询而不使用sp.PriorityRow? – zaza 2013-04-08 01:20:23