I am having problems with the following code and hope someone can explain 
this to me.  Here is the routine that is having the problems:

    Private Shared Sub LoadSubscriptionFromDataRow(ByVal s As Subscription, 
ByVal dr As DataRow)
        With dr
            With s
                .SubscriptionId = .Item(CN_SubscriptionId)
                .UserId = CType(.Item(CN_UserId), Integer)
                .BillToId = CType(.Item(CN_BillToId), Integer)
 *              .OrderDate = CType(.Item(CN_OrderDate), Date)
                .ProductId = .Item(CN_ProductId)
                .LicQty = CType(.Item(CN_LicQty), Short)
  *             .RenewalDate = CType(.Item(CN_RenewalDate), Nullable(Of Date))
                .LastInvType = .Item(CN_LastInvType)
                .LastInvSeq = CType(.Item(CN_LastInvSeq), Short)
                .AbaNo = .Item(CN_AbaNo)
                .TaxStatus = .Item(CN_TaxStatus)
                .BillingComment = .Item(CN_BillingComment)
 * *           .CancelDate = CType(.Item(CN_CancelDate), Nullable(Of Date))
                .CancelCode = .Item(CN_CancelCode)
 *              .LastMaintDate = CType(.Item(CN_LastMaintDate), Date)
            End With
        End With
    End Sub

Each of the lines flaged above throws an execption.  

Conversion from string "" to type 'Date' is not valid.
but upon examinatiopn of one of the data items, it is a valid date:
+dr.Item("OrderDate")	#5/23/1990# {Date}	Object
	Date	#5/23/1990#	Date
and the funny thing is that by changing the line to ....dr.item(... the 
exception goes away!  So, it must have someting to do with the 'with dr'.  
Also funny that the problem only occurs on 'Date' types.

On the line with 2 '**'s, the above exception changes to:

System.InvalidCastException was unhandled
  Message="Specified cast is not valid."

the value is System.VBNull.  I guess I have to handle the case where the 
date comming from the DB is null in some other way, but I thought this was 
the reason for Nullable(Of T).

-- 
Terry

"Terry" <TerryL@nospam.nospam> schrieb

> I am having problems with the following code and hope someone can
> explain this to me.  Here is the routine that is having the
> problems:
>
>    Private Shared Sub LoadSubscriptionFromDataRow(ByVal s As
> Subscription, ByVal dr As DataRow)
>        With dr
>            With s
>                .SubscriptionId = .Item(CN_SubscriptionId)
>                .UserId = CType(.Item(CN_UserId), Integer)
>                .BillToId = CType(.Item(CN_BillToId), Integer)
> *              .OrderDate = CType(.Item(CN_OrderDate), Date)
>                .ProductId = .Item(CN_ProductId)
>                .LicQty = CType(.Item(CN_LicQty), Short)
>  *             .RenewalDate = CType(.Item(CN_RenewalDate),
> Nullable(Of Date))                .LastInvType =
> .Item(CN_LastInvType)
>                .LastInvSeq = CType(.Item(CN_LastInvSeq), Short)
>                .AbaNo = .Item(CN_AbaNo)
>                .TaxStatus = .Item(CN_TaxStatus)
>                .BillingComment = .Item(CN_BillingComment)
> * *           .CancelDate = CType(.Item(CN_CancelDate), Nullable(Of
> Date))                .CancelCode = .Item(CN_CancelCode)
> *              .LastMaintDate = CType(.Item(CN_LastMaintDate), Date)
>            End With
>        End With
>    End Sub
>
> Each of the lines flaged above throws an execption.
>
> Conversion from string "" to type 'Date' is not valid.
> but upon examinatiopn of one of the data items, it is a valid date:
> +dr.Item("OrderDate") #5/23/1990# {Date} Object
> Date #5/23/1990# Date
> and the funny thing is that by changing the line to ....dr.item(...
> the exception goes away!


Not funny. You are nesting With blocks which doesn't makes sense in this
case.

With dr
   With s
      .OrderDate = CType(.Item(CN_OrderDate), Date)
   end with
end with

You are referring to s on the left and on the right side of the "=". The
DataRow is not used at all. So, this is the same as

s.OrderDate = CType(s.Item(CN_OrderDate), Date)

Probably the "Subscription" class has an Item property where you can pass a
Date but CN_OrderDate is a String. Therefore the error.



>  So, it must have someting to do with the
> 'with dr'. Also funny that the problem only occurs on 'Date' types.
>
> On the line with 2 '**'s, the above exception changes to:
>
> System.InvalidCastException was unhandled
>  Message="Specified cast is not valid."
>
> the value is System.VBNull.


System.DBNull.Value?


> I guess I have to handle the case where
> the date comming from the DB is null in some other way,

Correct

> but I
> thought this was the reason for Nullable(Of T).


Nullable has no relation to DBNull. In the Framework (and other languages), 
the term "Null" is used for "no reference", which is "Nothing" in VB. So, 
Nullable(Of Date) means that it can be either Nothing or a Date. It can 
never be DBNull.Value.
So,

    if DatabaseValue is dbnull.value then
        .NullableOfDateField = Nothing
    else
        .NullableOfDateField = CDate(DataBaseValue)
    end if


Armin

Hi Armin,
   Thanks for the quick reply.  Thats what I get for using someone elses 
code to start with.  S inherits from a class that has an Item property, and I 
missed that.  I am still confused as to why it is only with the date 
conversions that the problem shows up.
   On the second issue, thanks - got it.
-- 
Terry


"Armin Zingler" wrote:


> "Terry" <TerryL@nospam.nospam> schrieb
> > I am having problems with the following code and hope someone can
> > explain this to me.  Here is the routine that is having the
> > problems:
> >
> >    Private Shared Sub LoadSubscriptionFromDataRow(ByVal s As
> > Subscription, ByVal dr As DataRow)
> >        With dr
> >            With s
> >                .SubscriptionId = .Item(CN_SubscriptionId)
> >                .UserId = CType(.Item(CN_UserId), Integer)
> >                .BillToId = CType(.Item(CN_BillToId), Integer)
> > *              .OrderDate = CType(.Item(CN_OrderDate), Date)
> >                .ProductId = .Item(CN_ProductId)
> >                .LicQty = CType(.Item(CN_LicQty), Short)
> >  *             .RenewalDate = CType(.Item(CN_RenewalDate),
> > Nullable(Of Date))                .LastInvType =
> > .Item(CN_LastInvType)
> >                .LastInvSeq = CType(.Item(CN_LastInvSeq), Short)
> >                .AbaNo = .Item(CN_AbaNo)
> >                .TaxStatus = .Item(CN_TaxStatus)
> >                .BillingComment = .Item(CN_BillingComment)
> > * *           .CancelDate = CType(.Item(CN_CancelDate), Nullable(Of
> > Date))                .CancelCode = .Item(CN_CancelCode)
> > *              .LastMaintDate = CType(.Item(CN_LastMaintDate), Date)
> >            End With
> >        End With
> >    End Sub
> >
> > Each of the lines flaged above throws an execption.
> >
> > Conversion from string "" to type 'Date' is not valid.
> > but upon examinatiopn of one of the data items, it is a valid date:
> > +dr.Item("OrderDate") #5/23/1990# {Date} Object
> > Date #5/23/1990# Date
> > and the funny thing is that by changing the line to ....dr.item(...
> > the exception goes away!
> 
> Not funny. You are nesting With blocks which doesn't makes sense in this
> case.
> 
> With dr
>    With s
>       .OrderDate = CType(.Item(CN_OrderDate), Date)
>    end with
> end with
> 
> You are referring to s on the left and on the right side of the "=". The
> DataRow is not used at all. So, this is the same as
> 
> s.OrderDate = CType(s.Item(CN_OrderDate), Date)
> 
> Probably the "Subscription" class has an Item property where you can pass a
> Date but CN_OrderDate is a String. Therefore the error.
> 
> 
> >  So, it must have someting to do with the
> > 'with dr'. Also funny that the problem only occurs on 'Date' types.
> >
> > On the line with 2 '**'s, the above exception changes to:
> >
> > System.InvalidCastException was unhandled
> >  Message="Specified cast is not valid."
> >
> > the value is System.VBNull.
> 
> System.DBNull.Value?
> 
> > I guess I have to handle the case where
> > the date comming from the DB is null in some other way,
> 
> Correct
> 
> > but I
> > thought this was the reason for Nullable(Of T).
> 
> Nullable has no relation to DBNull. In the Framework (and other languages), 
> the term "Null" is used for "no reference", which is "Nothing" in VB. So, 
> Nullable(Of Date) means that it can be either Nothing or a Date. It can 
> never be DBNull.Value.
> So,
> 
>     if DatabaseValue is dbnull.value then
>         .NullableOfDateField = Nothing
>     else
>         .NullableOfDateField = CDate(DataBaseValue)
>     end if
> 
> 
> Armin
> 
> 

Hi Terry,


>  I am still confused as to why it is only with the date conversions that 

the problem shows up.

Perhaps other properties, such as 'Subscription', 'UserId', "BillTold" and 
ect in the Subscription instance have correct types and initial value. 

Hope this helps.

If you have any question, please feel free to let me know.

Sincerely,
Linda Liu
Microsoft Online Community Support

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