Question

I am running into this error. I see that the reason is because the average returned at times is 0.00 which from a data stand point is accurate. This SQL query works fine, but that is because it puts in 0.00 automatically.

LINQ complains and so I tried using DefaultIfEmpty() but it says it is expecting my ViewModel.

Dim ticketCounts = From t In queue _
   Where _
    (t.StatusId = 2) And _
    (t.CloseDate.Year = Convert.ToDateTime(DateTime.Now).Year) And _
    (t.ResolutionDays > 0)
   Group t By _
    Column1 = CType(t.CloseDate.Month, Integer), _
    Column2 = CType(t.CloseDate.ToString("MMMM"), String) _
    Into g = Group _
   Order By Column1 _
   Select _
    Id = Column1, _
    Month = Column2, _
    Critical = g.Where(Function(t) t.PriorityId = 1).DefaultIfEmpty().Average(Function(t) t.ResolutionDays), _
    High = g.Where(Function(t) t.PriorityId = 2).DefaultIfEmpty().Average(Function(t) t.ResolutionDays), _
    Normal = g.Where(Function(t) t.PriorityId = 3).DefaultIfEmpty().Average(Function(t) t.ResolutionDays), _
    Low = g.Where(Function(t) t.PriorityId = 4).DefaultIfEmpty().Average(Function(t) t.ResolutionDays), _
    Total = g.Where(Function(t) t.Id <> Nothing).DefaultIfEmpty().Average(Function(t) t.ResolutionDays)

UPDATED!
This is the SQL query doing the same thing I need VB to do.

SELECT
    DATENAME(MONTH,t.CloseDate) AS 'Month',
    AVG(CASE WHEN (t.PriorityId = 1) THEN CAST(t.ResolutionDays AS Decimal(18, 2)) ELSE 0 END) AS 'Critical',
    AVG(CASE WHEN (t.PriorityId = 2) THEN CAST(t.ResolutionDays AS Decimal(18, 2)) ELSE 0 END) AS 'High',
    AVG(CASE WHEN (t.PriorityId = 3) THEN CAST(t.ResolutionDays AS Decimal(18, 2)) ELSE 0 END) AS 'Normal',
    AVG(CASE WHEN (t.PriorityId = 4) THEN CAST(t.ResolutionDays AS Decimal(18, 2)) ELSE 0 END) AS 'Low',
    AVG(CAST(t.ResolutionDays AS Decimal(18, 2))) AS 'Monthly Average'
FROM
    tblMaintenanceTicket t
WHERE
    t.StatusId = 2
    AND YEAR(t.CloseDate) = year(getdate())
GROUP BY 
    MONTH(t.CloseDate),
    DATENAME(MONTH,t.CloseDate)
ORDER BY
    MONTH(t.CloseDate)

Answer 1

The problem is that all of the scalar LINQ methods (Average, Max, etc …) throw an exception if the input IEnumerable(Of T) doesn’t have any elements. It looks like the g.Where calls are resulting in an empty collection resulting in the exception.

What you may want to do is write a method which handles the empty case and returns a default value.