"Cast" error with VB code in .aspx page, with a twist...

[roy.anderson]

Error is thus: "Cast from type 'DBNull' to type 'String' is not valid."
Simple, right? Well, no (or at least not for me).

Here's a function, followed by the calling code below:

Function GetDetails(ByVa l x As String, ByVal y as String)
Dim conn As New SqlConnection
("server=localh ost;uid=blah;pw d=blah;database =test")
Dim strSQL As String
Dim ds As New DataSet()

strSQL = "SELECT firstv.ocean_ca r, firstv.nr,first v.equip "
strSQL &= "FROM firstv INNER JOIN "
strSQL &= "lla ON firstv.doc + firstv.po = lla.doc + lla.po "
strSQL &= "WHERE firstv.doc = " & x & "AND firstv.po = " & y

Dim da As New SqlDataAdapter( strSQL, conn)
da.Fill(ds, "firstv")
Return ds.Tables("firs tv")
End Function

Calling code:

<asp:DataGrid runat=server id=dgDetails
DataSource=<%#
GetDetails(cont ainer.dataitem( "doc"),containe r.dataitem("po" ))%>
AutoGenerateCol umns=false>
<Columns>
<asp:BoundColum n DataField="ocea n_car"
HeaderText="Car rier"></asp:BoundColumn >
<asp:BoundColum n DataField="nr" HeaderText="Boo king"></asp:BoundColumn >
<asp:BoundColum n DataField="Equi p"
HeaderText="Equ ip"></asp:BoundColumn >
</Columns>
</asp:DataGrid>
The error occurs on the very first line of the calling code above.
Naturally, I thought "ah, it must be pulling in nulls from the doc and
po fields in firstv and that must be the cause." So I opened Query
Analyzer and changed all the nulls (in every column) into blanks. Still
got the error so I went back to QA and changed them all to "xyz."
Still, I got the error!! I thought maybe it had to do with the "ByVal"
statement in the function and switched to ByRef... still no go. Anyone
have any tips, please?
Thanks! And yes, I am still am relatively new to .NET. ;)

[Chris, Master of All Things Insignificant]

I am not sure that I have an answer for you if your sure there are no nulls
coming through your sql. This may be just a hint for next time for you
then. This is how I would write the statement next time; at least I do when
I want to eliminate snulls as an issue.

strSQL = "SELECT IsNull(firstv.o cean_car, ''), IsNull(firstv.n r,
''),IsNull(firs tv.equip, '') "
strSQL &= "FROM firstv INNER JOIN "
strSQL &= "lla ON firstv.doc + firstv.po = lla.doc + lla.po "
strSQL &= "WHERE firstv.doc = " & x & "AND firstv.po = " & y

Chris

<ro**********@g mail.com> wrote in message
news:11******** **************@ f14g2000cwb.goo glegroups.com.. .

Error is thus: "Cast from type 'DBNull' to type 'String' is not valid."
Simple, right? Well, no (or at least not for me).

Here's a function, followed by the calling code below:

Function GetDetails(ByVa l x As String, ByVal y as String)
Dim conn As New SqlConnection
("server=localh ost;uid=blah;pw d=blah;database =test")
Dim strSQL As String
Dim ds As New DataSet()

strSQL = "SELECT firstv.ocean_ca r, firstv.nr,first v.equip "
strSQL &= "FROM firstv INNER JOIN "
strSQL &= "lla ON firstv.doc + firstv.po = lla.doc + lla.po "
strSQL &= "WHERE firstv.doc = " & x & "AND firstv.po = " & y

Dim da As New SqlDataAdapter( strSQL, conn)
da.Fill(ds, "firstv")
Return ds.Tables("firs tv")
End Function

Calling code:

<asp:DataGrid runat=server id=dgDetails
DataSource=<%#
GetDetails(cont ainer.dataitem( "doc"),containe r.dataitem("po" ))%>
AutoGenerateCol umns=false>
<Columns>
<asp:BoundColum n DataField="ocea n_car"
HeaderText="Car rier"></asp:BoundColumn >
<asp:BoundColum n DataField="nr" HeaderText="Boo king"></asp:BoundColumn >
<asp:BoundColum n DataField="Equi p"
HeaderText="Equ ip"></asp:BoundColumn >
</Columns>
</asp:DataGrid>
The error occurs on the very first line of the calling code above.
Naturally, I thought "ah, it must be pulling in nulls from the doc and
po fields in firstv and that must be the cause." So I opened Query
Analyzer and changed all the nulls (in every column) into blanks. Still
got the error so I went back to QA and changed them all to "xyz."
Still, I got the error!! I thought maybe it had to do with the "ByVal"
statement in the function and switched to ByRef... still no go. Anyone
have any tips, please?
Thanks! And yes, I am still am relatively new to .NET. ;)

[Roy]

Hey Chris,

Thanks for the input. In sheer desperation I popped your code there in
place of mine. Same error on the same line. *sigh*

[Roy]

Actually... something else occurred to me. Could the error perhaps be a
red herring? As in, assuming either "x" or "y" contained blank data,
could the join or where part of the sql statement (within the function)
be causing the "cast" error?

Would the compiler recognize the empty x or y values as '' or ....?
Anyone know how the compiler would interpret blanks in this case?

[Kerry Moorman]

Roy,

Since x and y are strings, when you are integrating them into your SQL Where
clause I think you need to surround them with single-quote delimiters:

strSQL &= "WHERE firstv.doc = '" & x & "' AND firstv.po = '" & y & "'"

Kerry Moorman
"ro**********@g mail.com" wrote:

Error is thus: "Cast from type 'DBNull' to type 'String' is not valid."
Simple, right? Well, no (or at least not for me).

Here's a function, followed by the calling code below:

Function GetDetails(ByVa l x As String, ByVal y as String)
Dim conn As New SqlConnection
("server=localh ost;uid=blah;pw d=blah;database =test")
Dim strSQL As String
Dim ds As New DataSet()

strSQL = "SELECT firstv.ocean_ca r, firstv.nr,first v.equip "
strSQL &= "FROM firstv INNER JOIN "
strSQL &= "lla ON firstv.doc + firstv.po = lla.doc + lla.po "
strSQL &= "WHERE firstv.doc = " & x & "AND firstv.po = " & y

Dim da As New SqlDataAdapter( strSQL, conn)
da.Fill(ds, "firstv")
Return ds.Tables("firs tv")
End Function

Calling code:

<asp:DataGrid runat=server id=dgDetails
DataSource=<%#
GetDetails(cont ainer.dataitem( "doc"),containe r.dataitem("po" ))%>
AutoGenerateCol umns=false>
<Columns>
<asp:BoundColum n DataField="ocea n_car"
HeaderText="Car rier"></asp:BoundColumn >
<asp:BoundColum n DataField="nr" HeaderText="Boo king"></asp:BoundColumn >
<asp:BoundColum n DataField="Equi p"
HeaderText="Equ ip"></asp:BoundColumn >
</Columns>
</asp:DataGrid>
The error occurs on the very first line of the calling code above.
Naturally, I thought "ah, it must be pulling in nulls from the doc and
po fields in firstv and that must be the cause." So I opened Query
Analyzer and changed all the nulls (in every column) into blanks. Still
got the error so I went back to QA and changed them all to "xyz."
Still, I got the error!! I thought maybe it had to do with the "ByVal"
statement in the function and switched to ByRef... still no go. Anyone
have any tips, please?
Thanks! And yes, I am still am relatively new to .NET. ;)

[Chris, Master of All Things Insignificant]

Good point.

Chris

"Kerry Moorman" <Ke**********@d iscussions.micr osoft.com> wrote in message
news:85******** *************** ***********@mic rosoft.com...

Roy,

Since x and y are strings, when you are integrating them into your SQL
Where
clause I think you need to surround them with single-quote delimiters:

strSQL &= "WHERE firstv.doc = '" & x & "' AND firstv.po = '" & y & "'"

Kerry Moorman
"ro**********@g mail.com" wrote:

Error is thus: "Cast from type 'DBNull' to type 'String' is not valid."
Simple, right? Well, no (or at least not for me).

Here's a function, followed by the calling code below:

Function GetDetails(ByVa l x As String, ByVal y as String)
Dim conn As New SqlConnection
("server=localh ost;uid=blah;pw d=blah;database =test")
Dim strSQL As String
Dim ds As New DataSet()

strSQL = "SELECT firstv.ocean_ca r, firstv.nr,first v.equip "
strSQL &= "FROM firstv INNER JOIN "
strSQL &= "lla ON firstv.doc + firstv.po = lla.doc + lla.po "
strSQL &= "WHERE firstv.doc = " & x & "AND firstv.po = " & y

Dim da As New SqlDataAdapter( strSQL, conn)
da.Fill(ds, "firstv")
Return ds.Tables("firs tv")
End Function

Calling code:

<asp:DataGrid runat=server id=dgDetails
DataSource=<%#
GetDetails(cont ainer.dataitem( "doc"),containe r.dataitem("po" ))%>
AutoGenerateCol umns=false>
<Columns>
<asp:BoundColum n DataField="ocea n_car"
HeaderText="Car rier"></asp:BoundColumn >
<asp:BoundColum n DataField="nr" HeaderText="Boo king"></asp:BoundColumn >
<asp:BoundColum n DataField="Equi p"
HeaderText="Equ ip"></asp:BoundColumn >
</Columns>
</asp:DataGrid>
The error occurs on the very first line of the calling code above.
Naturally, I thought "ah, it must be pulling in nulls from the doc and
po fields in firstv and that must be the cause." So I opened Query
Analyzer and changed all the nulls (in every column) into blanks. Still
got the error so I went back to QA and changed them all to "xyz."
Still, I got the error!! I thought maybe it had to do with the "ByVal"
statement in the function and switched to ByRef... still no go. Anyone
have any tips, please?
Thanks! And yes, I am still am relatively new to .NET. ;)

[Roy]

Thanks for the input Kerry, but dishearteningly enough, even after
modifying the code as you suggested, the exact same error occurs.
*sigh*

[Kerry Moorman]

Roy,

When you call the function like this:

GetDetails(cont ainer.dataitem( "doc"),containe r.dataitem("po" ))

might either container.datai tem("doc") or container.datai tem("po") be null?

Kerry Moorman
"Roy" wrote:

Thanks for the input Kerry, but dishearteningly enough, even after
modifying the code as you suggested, the exact same error occurs.
*sigh*

[Roy]

Yes on both counts.

[Roy]

Correction. I misread what you were saying. As of now, the table those
two fields are extracted from (firstv) contains absolutely no "NULL"
values at all. There are blank values here and there, but no "NULL."