问题

As per a previous question, I've got the following LINQ expression.

Events.Where(Function(e) e.EventDate >= Date.Today) _
            .OrderByDescending(Function(e) (((e.EventVotes.Sum(Function(s) s.Vote)) * 2) + (e.Comments.Count))) _
            .Skip(0) _
            .Take(5)

Which converts to the following SQL

-- Region Parameters
DECLARE @p0 DateTime2 = '2011-01-17 00:00:00.0000000'
DECLARE @p1 Int = 2
DECLARE @p2 Int = 0
DECLARE @p3 Int = 5
-- EndRegion
SELECT [t3].[ID], [t3].[UserID], [t3].[RegionID], [t3].[LocationID], [t3].[Title], [t3].[Description], [t3].[EventDate], [t3].[URL], [t3].[Phone], [t3].[TicketPriceLow], [t3].[TicketPriceHigh], [t3].[DatePosted], [t3].[isHighlighted]
FROM (
    SELECT ROW_NUMBER() OVER (ORDER BY (((
        SELECT SUM([t1].[Vote])
        FROM [dbo].[EventVotes] AS [t1]
        WHERE [t1].[EventID] = [t0].[ID]
        )) * @p1) + ((
        SELECT COUNT(*)
        FROM [dbo].[Comments] AS [t2]
        WHERE [t2].[EventID] = [t0].[ID]
        )) DESC) AS [ROW_NUMBER], [t0].[ID], [t0].[UserID], [t0].[RegionID], [t0].[LocationID], [t0].[Title], [t0].[Description], [t0].[EventDate], [t0].[URL], [t0].[Phone], [t0].[TicketPriceLow], [t0].[TicketPriceHigh], [t0].[DatePosted], [t0].[isHighlighted]
    FROM [dbo].[Events] AS [t0]
    WHERE [t0].[EventDate] >= @p0
    ) AS [t3]
WHERE [t3].[ROW_NUMBER] BETWEEN @p2 + 1 AND @p2 + @p3
ORDER BY [t3].[ROW_NUMBER]

My problem now is when it comes to ordering when some events don't have any votes or comments.

Here is what the EventVotes table looks like (in it's entirety)

| UserID | EventID | Vote |    
| 1      | 51      | 1    |   
| 1      | 52      | 1    |   
| 2      | 52      | 1    |   
| 1      | 53      | 1    |   
| 2      | 53      | -1   |   
| 3      | 53      | -1   |

The Comments table is completely empty, so since we're just doing a Count on it, we can assume that everything comes back Null.

Now when I run the query above, the result order is as follows

52
51
53
1
2
3

When it "should" be

52
51
1
2
3
53

because event number 53 has a vote count of "-1" while event numbers 1, 2, and 3 have a vote count of "0"

Can anyone help figure out how to enhance the Linq expression to account for events that haven't been voted on?

Here's a screenshot

EDIT:

Ok, so I've simplified the query in LinqPad to this, and the result is that I only get three results.

Events.OrderByDescending(Function(e) (((e.EventVotes.Sum(Function(s) s.Vote)) * 2) + (e.Comments.Count)))

What this is telling me is that the orderby is only grabbing those three results (51, 52, 53), then it appends the rest of the results AFTER the order clause. I need to figure out a way to include the rest of the "null" results in the Lambda expression.

回答1:

Here's a C# solution. I tried to translate it into VB, but my VB skills (and desire to learn it, honestly) are nil, and I gave up. I'll try to highlight the critical points to help with the translation.

Here's the full statement:

context.Events.OrderByDescending(e => (((e.EventVotes.Sum(s => (int?)s.Vote) ?? 0) * 2) + e.Comments.Count))

What's critical is that s.Vote is first cast to a nullable integer so that the result of Sum() will be a nullable integer. A nullable result allows you to explicitly check for null and use zero for the rest of calculation if the result was indeed null.

For VB translation purposes, ?? is a C# null-coalesce operator where (for example) myNullableIntVar ?? 0 evaluates to the value of myNullableIntVar, or if it is null, then 0.

Here's the SQL generated by the above statement, FWIW:

exec sp_executesql N'SELECT [t0].[EventID], [t0].[Name]
FROM [dbo].[Events] AS [t0]
ORDER BY ((COALESCE((
    SELECT SUM([t2].[value])
    FROM (
        SELECT [t1].[Vote] AS [value], [t1].[EventID]
        FROM [dbo].[EventVotes] AS [t1]
        ) AS [t2]
    WHERE [t2].[EventID] = [t0].[EventID]
    ),@p0)) * @p1) + ((
    SELECT COUNT(*)
    FROM [dbo].[Comments] AS [t3]
    WHERE [t3].[EventID] = [t0].[EventID]
    )) DESC',N'@p0 int,@p1 int',@p0=0,@p1=2

Edit by rockinthesixstring

I've added the VB.NET version below - This works exactly as expected. I tried to do a DirectCast(s.Vote, Integer?) but it threw an error saying that Integer cannot be converted to Integer?, So I had to take this approach.

Events.OrderByDescending(Function(e) (((If(e.EventVotes.Sum(Function(s) s.Vote),
                                           e.EventVotes.Sum(Function(s) s.Vote),
                                           0)) * 2) + e.Comments.Count))

Which resulted in this SQL Query

-- Region Parameters
DECLARE @p0 Int = 0
DECLARE @p1 Int = 2
-- EndRegion
SELECT [t0].[ID], [t0].[UserID], [t0].[RegionID], [t0].[LocationID], [t0].[Title], [t0].[Description], [t0].[EventDate], [t0].[URL], [t0].[Phone], [t0].[TicketPriceLow], [t0].[TicketPriceHigh], [t0].[DatePosted], [t0].[isHighlighted]
FROM [dbo].[Events] AS [t0]
ORDER BY ((
    (CASE 
        WHEN (CONVERT(Bit,(
            SELECT SUM([t1].[Vote])
            FROM [dbo].[EventVotes] AS [t1]
            WHERE [t1].[EventID] = [t0].[ID]
            ))) = 1 THEN (
            SELECT SUM([t2].[Vote])
            FROM [dbo].[EventVotes] AS [t2]
            WHERE [t2].[EventID] = [t0].[ID]
            )
        ELSE @p0
     END)) * @p1) + ((
    SELECT COUNT(*)
    FROM [dbo].[Comments] AS [t3]
    WHERE [t3].[EventID] = [t0].[ID]
    )) DESC

来源：https://stackoverflow.com/questions/4719163/linq-how-to-orderby-the-sum-of-one-table-and-the-count-of-another

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