VB IF statement to ask if NULL then apply default image instead - sql

Question

Inherited a VB website and am new to vb programming, so steep learning curve.
I have a site that searches and list all currently available cars in the UK for a leasing company.
the vehicle data is provided by an external comapany and links all the tech specs etc and images to a keyID. However...
If the vehicle has not been assigned an image it is not counted or displayed. I want to add an IF statement so that if the ImageId is Null then it will display a default 'awaiting image' jpg and would therefore still be listed to the public.
the page is http://www.carmyke.co.uk/search_prices.aspx with the 'Vans' dropping the most from the list.
I have included the code I think I need to update.
I think I need an IF statement for the .ImageId that if the SQL returns NULL then it uses a default image located in the same folder as defined by the appsettings
Hope this makes sense!?
<--- THE CODE --->
#Region "Methods"
Private Function GetVehicle(ByVal SearchBy As SearchBy, _
ByVal SearchText As String) As Data.LeasingPrices.Vehicle
Dim _Vehicle As New Data.LeasingPrices.Vehicle
Try
Dim _SQL As New Net.SQL
_SQL.AppendSQL("SELECT TOP 1 * ")
_SQL.AppendSQL("FROM vw_carmyke_Rates_Business ")
_SQL.AppendSQL("LEFT OUTER JOIN carmyke_SpecialOffers ON vw_carmyke_Rates_Business.CVehicleId = carmyke_SpecialOffers.CVehicleId ")
Select Case SearchBy
Case Hydrate.SearchBy.Make
_SQL.AppendSQL("WHERE Make = #SearchText ")
Case Hydrate.SearchBy.Model
_SQL.AppendSQL("WHERE MakeModel = #SearchText ")
Case Hydrate.SearchBy.Derivative
_SQL.AppendSQL("WHERE MakeModelDerivative = #SearchText ")
End Select
_SQL.AppendSQL("ORDER BY Rental_48_40;")
_SQL.AddParameter("#SearchText", SearchText, SqlDbType.VarChar)
_SQL.ConnectReader()
If _SQL.Validation.NoErrors Then
If _SQL.Reader.Read() Then
With _Vehicle
.CVehicleId = _SQL.Reader.SQLString("CVehicleId").ToInteger()
.Van = _SQL.Reader.SQLString("BodyStyle").Contains("Van")
.Make = _SQL.Reader.SQLString("Make")
.Model = _SQL.Reader.SQLString("Model")
.Derivative = _SQL.Reader.SQLString("Derivative")
.ImageId = _SQL.Reader.SQLString("ImageId") & ".jpg"
.Co2 = _SQL.Reader.SQLString("Co2").ToInteger()
.P11d = _SQL.Reader.SQLString("P11d").ToDouble()
.Business = _SQL.Reader.SQLString("Business").ToBoolean()
.Personal = _SQL.Reader.SQLString("Personal").ToBoolean()
.Details = _SQL.Reader.SQLString("Details")
.OfferPrice = _SQL.Reader.SQLString("OfferPrice").ToDouble()
If .OfferPrice = 0 Then _
.OfferPrice = _SQL.Reader.SQLString("Offer_48_40").ToDouble()
If .OfferPrice = 0 Then _
.OfferPrice = _SQL.Reader.SQLString("Rental_48_40").ToDouble()
.Commercial = _SQL.Reader.SQLString("Commercial").ToBoolean()
.Offer_24_20 = _SQL.Reader.SQLString("Offer_24_20").ToDouble()
.Offer_24_40 = _SQL.Reader.SQLString("Offer_24_40").ToDouble()
.Offer_24_60 = _SQL.Reader.SQLString("Offer_24_60").ToDouble()
.Offer_36_30 = _SQL.Reader.SQLString("Offer_36_30").ToDouble()
.Offer_36_60 = _SQL.Reader.SQLString("Offer_36_60").ToDouble()
.Offer_36_90 = _SQL.Reader.SQLString("Offer_36_90").ToDouble()
.Offer_48_40 = _SQL.Reader.SQLString("Offer_48_40").ToDouble()
.Offer_48_80 = _SQL.Reader.SQLString("Offer_48_80").ToDouble()
.Offer_48_120 = _SQL.Reader.SQLString("Offer_48_120").ToDouble()
If .Offer_24_20 = -1 Then
.Rental_24_20 = 0
ElseIf .Offer_24_20 > 0 Then
.Rental_24_20 = .Offer_24_20
Else
.Rental_24_20 = _SQL.Reader.SQLString("Rental_24_20").ToDouble()
End If
If .Offer_24_40 = -1 Then
.Rental_24_40 = 0
ElseIf .Offer_24_40 > 0 Then
.Rental_24_40 = .Offer_24_40
Else
.Rental_24_40 = _SQL.Reader.SQLString("Rental_24_40").ToDouble()
End If
If .Offer_24_60 = -1 Then
.Rental_24_60 = 0
ElseIf .Offer_24_60 > 0 Then
.Rental_24_60 = .Offer_24_60
Else
.Rental_24_60 = _SQL.Reader.SQLString("Rental_24_60").ToDouble()
End If
If .Offer_36_30 = -1 Then
.Rental_36_30 = 0
ElseIf .Offer_36_30 > 0 Then
.Rental_36_30 = .Offer_36_30
Else
.Rental_36_30 = _SQL.Reader.SQLString("Rental_36_30").ToDouble()
End If
If .Offer_36_60 = -1 Then
.Rental_36_60 = 0
ElseIf .Offer_36_60 > 0 Then
.Rental_36_60 = .Offer_36_60
Else
.Rental_36_60 = _SQL.Reader.SQLString("Rental_36_60").ToDouble()
End If
If .Offer_36_90 = -1 Then
.Rental_36_90 = 0
ElseIf .Offer_36_90 > 0 Then
.Rental_36_90 = .Offer_36_90
Else
.Rental_36_90 = _SQL.Reader.SQLString("Rental_36_90").ToDouble()
End If
If .Offer_48_40 = -1 Then
.Rental_48_40 = 0
ElseIf .Offer_48_40 > 0 Then
.Rental_48_40 = .Offer_48_40
Else
.Rental_48_40 = _SQL.Reader.SQLString("Rental_48_40").ToDouble()
End If
If .Offer_48_80 = -1 Then
.Rental_48_80 = 0
ElseIf .Offer_48_80 > 0 Then
.Rental_48_80 = .Offer_48_80
Else
.Rental_48_80 = _SQL.Reader.SQLString("Rental_48_80").ToDouble()
End If
If .Offer_48_120 = -1 Then
.Rental_48_120 = 0
ElseIf .Offer_48_120 > 0 Then
.Rental_48_120 = .Offer_48_120
Else
.Rental_48_120 = _SQL.Reader.SQLString("Rental_48_120").ToDouble()
End If
End With
Else
_Vehicle = Nothing
End If
Else
_Vehicle = Nothing
End If
_SQL.DisconnectReader()
Catch
_Vehicle = Nothing
End Try
Return _Vehicle
End Function
Public Function Vehicle(ByVal SearchText As String) As Data.LeasingPrices.Vehicle
Dim _Vehicle As New Data.LeasingPrices.Vehicle
_Vehicle = GetVehicle(Hydrate.SearchBy.Derivative, SearchText)
If _Vehicle Is Nothing Then
_Vehicle = GetVehicle(Hydrate.SearchBy.Model, SearchText)
End If
If _Vehicle Is Nothing Then
_Vehicle = GetVehicle(Hydrate.SearchBy.Make, SearchText)
End If
Return _Vehicle
End Function
Private Function GetSearchOption(ByVal SearchOption As String) As String
Dim _GetSearchOption As String = ""
Try
If Not HttpContext.Current.Session(SearchOption) Is Nothing Then _
_GetSearchOption = HttpContext.Current.Session(SearchOption)
Catch
_GetSearchOption = ""
End Try
Return _GetSearchOption
End Function
Public Function SearchOptions() As Data.LeasingPrices.SearchOptions
Dim _SearchOptions As New Data.LeasingPrices.SearchOptions
Try
With _SearchOptions
.FourByFour = GetSearchOption("FourByFour").ToBoolean()
.CityCar = GetSearchOption("CityCar").ToBoolean()
.Coupe = GetSearchOption("Coupe").ToBoolean()
.Estate = GetSearchOption("Estate").ToBoolean()
.Hatchback = GetSearchOption("Hatchback").ToBoolean()
.MPV = GetSearchOption("MPV").ToBoolean()
.Saloon = GetSearchOption("Saloon").ToBoolean()
.Sports = GetSearchOption("Sports").ToBoolean()
.Van = GetSearchOption("Van").ToBoolean()
.RentalFrom = GetSearchOption("RentalFrom").ToInteger()
.RentalTo = GetSearchOption("RentalTo").ToInteger()
If .RentalFrom = 0 And .RentalTo = 0 Then
.RentalFrom = Data.LeasingPrices.SearchOptions.DefaultRentalFrom
.RentalTo = Data.LeasingPrices.SearchOptions.DefaultRentalTo
End If
End With
Catch
_SearchOptions = Nothing
End Try
Return _SearchOptions
End Function
#End Region
#Region "Constructors"
Public Sub New()
End Sub
#End Region
End Class
End Namespace

Answer 1

I'm not familiar with the Net.SQL entity you're using, but it is usual to use something like the Convert.IsDBNull Method to check for a NULL database value.
An alternative is to use COALESCE in the query, like
SELECT TOP 1 [CVehicleId], ..more columns.., COALESCE([ImageId], 'AwaitingImage'), ..remaining columns..
You should really explicitly specify the columns, and put the column names in square brackets so that if you accidentally have a column name which happens to be an SQL keyword then it doesn't mistake it for a keyword.