Question

How can I group result of a LINQ to SQL query by hours considering that the column type is DateTime?

Answer 1

Here’s a solution for technical hours (context-less).

var query = myDC.Orders     .GroupBy(x => x.OrderDate.Hour)     .Select(g => new {         Hour = g.Key,         Amount = g.Sum(x => x.OrderAmount)     }); 

Which generates this:

SELECT SUM([t1].[OrderAmount]) AS [Amount], [t1].[value] AS [Hour] FROM (     SELECT DATEPART(Hour, [t0].[OrderDate]) AS [value], [t0].[OrderAmount]     FROM [dbo].[Orders] AS [t0]     ) AS [t1] GROUP BY [t1].[value] 

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Here’s a solution for business hours (context-ful) .

DateTime zeroDate = new DateTime(2008, 1, 1);  var query = myDC.Orders     .GroupBy(x => System.Data.Linq.SqlClient.SqlMethods.DateDiffHour(zeroDate, x.OrderDate)     )     .Select(g => new { Hours = g.Key, Amount = g.Sum(x => x.OrderAmount) })     .Select(x => new { Hour = zeroDate.AddHours(x.Hours), Amount = x.Amount}); 

Which generates this:

SELECT DATEADD(ms, (CONVERT(BigInt,(CONVERT(Float,[t2].[value2])) * 3600000)) % 86400000, DATEADD(day, (CONVERT(BigInt,(CONVERT(Float,[t2].[value2])) * 3600000)) / 86400000, @p1)) AS [Hour], [t2].[value] AS [Amount] FROM (     SELECT SUM([t1].[OrderAmount]) AS [value], [t1].[value] AS [value2]     FROM (         SELECT DATEDIFF(Hour, @p0, [t0].[OrderDate]) AS [value], [t0].[OrderAmount]         FROM [dbo].[Orders] AS [t0]         ) AS [t1]     GROUP BY [t1].[value]     ) AS [t2] 

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Ugh – that bigint/float/milliseconds stuff is ugly and hard to verify. I prefer doing the addition back on the client side:

var results = myDC.Orders     .GroupBy(x => System.Data.Linq.SqlClient.SqlMethods.DateDiffHour(zeroDate, x.OrderDate)     )     .Select(g => new { Hours = g.Key, Amount = g.Sum(x => x.OrderAmount) })     .ToList()     .Select(x => new { Hour = zeroDate.AddHours(x.Hours), Amount = x.Amount}); 

Which generates this:

SELECT SUM([t1].[OrderAmount]) AS [Amount], [t1].[value] AS [Hours] FROM (     SELECT DATEDIFF(Hour, @p0, [t0].[OrderDate]) AS [value], [t0].[OrderAmount]     FROM [dbo].[Orders] AS [t0]     ) AS [t1] GROUP BY [t1].[value] 

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And here’s a third way of doing the contextful hours. This one is very c# friendly, but there’s string logic in the database (yuck).

var query = myDC.Orders     .GroupBy(x => new DateTime(x.OrderDate.Year, x.OrderDate.Month, x.OrderDate.Day, x.OrderDate.Hour, 0, 0))     .Select(g => new { Hour = g.Key, Amount = g.Sum(x => x.OrderAmount) }); 

Which generates

SELECT SUM([t1].[OrderAmount]) AS [Amount], [t1].[value] AS [Hour] FROM (     SELECT CONVERT(DATETIME, (CONVERT(NCHAR(4), DATEPART(Year, [t0].[OrderDate])) + ('-' + (CONVERT(NCHAR(2), DATEPART(Month, [t0].[OrderDate])) + ('-' + CONVERT(NCHAR(2), DATEPART(Day, [t0].[OrderDate])))))) + (' ' + (CONVERT(NCHAR(2), DATEPART(Hour, [t0].[OrderDate])) + (':' + (CONVERT(NCHAR(2), @p0) + (':' + CONVERT(NCHAR(2), @p1)))))), 120) AS [value], [t0].[OrderAmount]     FROM [dbo].[Orders] AS [t0]     ) AS [t1] GROUP BY [t1].[value]