无法将SQL查询转换为实体框架vb.net

Question

Disclaimer: may be long post

There is a lot of questions like this, and I am not quite happy to join the pack but yet , I am having a table which contains several rows and each they have effective dates, my sql query will fetch the latest records based on the effective date

select * from TblTaxmasters

i am using this query to get desired result

select * FROM (select t1.id,t1.shortcode,t1.rev_no,t1.percentage,t1.effectivedate startdate, isnull(MIN(t2.effectivedate),getdate()+1) as enddate FROM tbltaxmaster t1 LEFT
OUTER JOIN tbltaxmaster t2 on t1.id=t2.id AND t1.effectivedate < t2.effectivedate 
GROUP BY t1.id,t1.shortcode,t1.effectivedate,t1.rev_no,t1.percentage ) tx where '2014-05-01' BETWEEN tx.startdate AND tx.enddate 

The output is

now i am trying to convert this query against entity framework dbcontext in vb.net winforms 4.0

this is what i tried

Dim tomm = DateTime.Today.AddDays(1)
Dim mydate = DateTime.Today
Dim tax = (From t In (From t1 In tblTaxmasters
                                    From t2 In tblTaxmasters
                                    Where t1.id = t2.id And t1.effectivedate < t2.effectivedate
                                    Select New With {.id = t1.id, .shortcode = t1.shortcode, .maxdate = t1.effectivedate, .mindate = If(t2.effectivedate.HasValue, t2.effectivedate, tomm), .percentage = t1.percentage, .revno = t1.rev_no})
                                Where mydate >= t.mindate And mydate <= t.maxdate Select New With {t.shortcode, t.id, t.percentage, t.revno}).ToList()

and it told me

nothing

no result , then i tried the same thing with linqpad and it shows query executed successfully but no results. I checked the sql output and here what i get

    -- Region Parameters
DECLARE @p0 DateTime = '2014-05-10 00:00:00.000'
DECLARE @p1 DateTime = '2014-05-09 00:00:00.000'
DECLARE @p2 DateTime = '2014-05-09 00:00:00.000'
-- EndRegion
SELECT [t2].[shortcode], [t2].[id], [t2].[percentage], [t2].[rev_no] AS [revno]
FROM (
    SELECT [t0].[id], [t0].[shortcode], [t0].[effectivedate], 
        (CASE 
            WHEN [t1].[effectivedate] IS NOT NULL THEN [t1].[effectivedate]
            ELSE @p0
         END) AS [value], [t0].[percentage], [t0].[rev_no], [t1].[id] AS [id2], [t1].[effectivedate] AS [effectivedate2]
    FROM [tblTaxmaster] AS [t0], [tblTaxmaster] AS [t1]
    ) AS [t2]
WHERE (@p1 >= [t2].[value]) AND (@p2 <= [t2].[effectivedate]) AND ([t2].[id] = [t2].[id2]) AND ([t2].[effectivedate] < [t2].[effectivedate2])

obviously something

lost in translation

so anybody can point me which way to move forward.

Answer 1

@Mark, Thanks for pointing the right direction, actually i have to tweak it with the help of this link in another forum. But glad both worked out, so here is what i have did finally

Dim tax = From c In ctx.tblTaxmasters
                        Group c By c.id Into g = Group
                    Select g.OrderByDescending(Function(x) x.effectivedate).FirstOrDefault()


            Dim mytax = tax.ToList()

Thanks for the help

Today accidentally when i searched inside msdn there are loads of questions based on the same topic is already available, and most prominent answers are from stack over flow. And it digs deeper than what i thought , it leads me to vb and c# compiler difference of anonymous types the key keyword etc. one surprising fact is that msdn search is spot on than google.