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How to use Request.QueryString with dynamic variables ?

Posted on 2009-05-15
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Last Modified: 2013-11-07
HI

A web catalog uses local variables in order to filter and index products but sometimes would be necessary create dynamically values using a query string like: catalog.aspx?var1=val1&var2=val2...., and sometimes just will be: catalog.aspx (without any query string)

How could I implement dynamic variables in order to avoid errors in case they doesn´t exist ?

Thanks.
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Question by:dimensionav
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LVL 29

Expert Comment

by:David H.H.Lee
ID: 24393099
Hi dimensionav,
>>..How could I implement dynamic variables in order to avoid errors in case they doesn´t exist ?
It sound like pre-caution step to avoid any malicious input from user during the application accessing the dynamic variables that created. How is your existing code flow look like and any errors that return at the moment during the missing of dynamic variable's existances?
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Author Comment

by:dimensionav
ID: 24393179
HI

I have the attached code at the very top of script area but when there´s nothing to get from query string, I got an error: REQUEST NOT AVAILABLE IN THIS CONTEXT.

And as you said, how to protect from malicious code?
Thanks.
    Dim GetIdCategoria As String = (Request.QueryString("idcategoria")).Trim
    Dim GetIdSubcategoria As String = (Request.QueryString("subcategoria")).Trim
    Dim GetBusqueda As String = (Request.QueryString("busqueda")).Trim

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LVL 29

Expert Comment

by:David H.H.Lee
ID: 24393288
Hi dimensionav,
You can write a custom function to cater this malicious input, you can enhance it on your need.
eg:
Dim GetIdCategoria As String = GetQueryParams(Request.QueryString("idcategoria"))

 Function GetQueryParams(ByVal str As String, Optional ByVal strBlank As String = "") As String
        Dim s As String = strBlank
        If Not String.IsNullOrEmpty(str) Then
            s = str.ToString.Trim
        End If

        Return s
    End Function
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Author Comment

by:dimensionav
ID: 24393454
if the form doesn´t receive any query string variable the code is still giving the same error.
I have tried to call the file as catalogo.aspx

Thanks.
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LVL 29

Expert Comment

by:David H.H.Lee
ID: 24393516
Hi dimensionav,
The posted code is working fine under test site. Do you apply it under any CMS application?
Try check if this article helps:
http://cosier.wordpress.com/2008/02/15/request-is-not-available-in-this-context-request-not-available-at-application_start-in-iis7/
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LVL 7

Accepted Solution

by:
ajolly earned 500 total points
ID: 24401078
try this:
Dim GetIdCategoria As String =""
If Not IsNothing Request.QueryString("idcategoria") then
    GetIdCategoria = Request.QueryString("idcategoria")
End If

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