ASP Primer:

Making a Request

by Curtis Dicken

Use these bookmarks
to jump around the tutorial:

[Request.Cookies:
Getting Stuff Out of a Cookie

[The
Handy Dandy Session Variable]

[Request.QuryString:
Passing Information Along]

[What’s
Next?]

Request.QueryString:
Passing Information Along

Now that you know how to
pass information from one page to another using a Session Variable, let’s talk
about a different way to pass information along.

Request.QueryString
is used to retrieve information directly from the URL. Let’s take a real-life
situation and see how Request.QueryString works:

Let’s say you have a
website that has several different game reviews on it. On your home page you
have 6 different links to different reviews. Instead of creating 6 separate
pages, 1 for each review, you decide that you are going to use a single ASP page
to display the reviews. The only problem is knowing which review to display.

The solution that you
come up with uses Request.QueryString. You determine that the easiest way
to let your review display page know what review to display is to send the
user’s selection through the URL.

You first create your 6
different review links on your home page that look something like this:

<A href="reviews.asp?reviewid=game1">Review
1</A>

There is really nothing
special about how the link is created, it’s just standard HTML. The special part
is how you construct the URL. As you can see, the first part of the link is
quite normal, just the name of the page that we want to go to. Then there is the
question mark. The question mark is used to differentiate between the page path
and the information that we are passing along. Next is the identifier for our
information, "gameid". Each item that you pass through a URL must have it’s own
unique identifier within the URL in order for Request.QueryString to do
its job. Finally, we set our unique identifier equal to whatever information we
want to pass along, which is "game1" in this case.

So, what if I want to
send more than one piece of information via a URL?

You can send as much
information as you like by using the ampersand to connect the pieces. Here’s an
example:

<A href="link.asp?item1=yes&item2=no">Link</A>

Now that you understand
how to send the information in a URL, let’s take a look out getting the
information out using Request.QueryString. In order to best demonstrate
how Request.QueryString works I’ll give you the code for the game review
example we started above:

<% Option Explicit %>

…

<% Select Case
Request.QueryString("gameid") %>

    <%
Case "game1" %>

       
<% Response.Write "This is the game 1 review …" %>

    <%
Case "game2" %>

       
<% Response.Write "This is the game 2 review …" %>

    <%
Case "game3" %>

       
<% Response.Write "This is the game 3 review …" %>

    <%
Case "game4" %>

       
<% Response.Write "This is the game 4 review …" %>

    <%
Case "game5" %>

       
<% Response.Write "This is the game 5 review …" %>

    <%
Case "game6" %>

       
<% Response.Write "This is the game 6 review …" %>

<% End Select %>

We use a Case statement
to determine which review needs to be displayed. You’ll notice the
Request.QueryString in the beginning of the Case statement. To retrieve a
value from a URL, all you need to know is the unique identifier that is being
used. In our case, the only unique identifier that we are using is "gameid".

What happens if I
misspell my unique identifier or forget to add it to the URL?

If
Request.QueryString doesn’t find the unique identifier that you are looking
for it will simply return an empty string value, i.e. "".

Though it is a very
simple process to send information from page to page via the URL, there are a
few things you need to be aware of:

• Any information sent via
  a URL is not secure. Whatever you do, don’t ever pass credit card numbers
  or any other sensitive information along in a URL.

• It’s not like a Session
  Variable. Session Variables keep their value from page to page no matter how
  many pages the user jumps around to. With Request.QueryString, the value
  must be passed in the URL each time you move from one page to another.

• URL’s are very temper
  mental about the way they are structured. If you are unsure whether the URL that
  you are using is compliant, you can use a spiffy little function called
  Server.URLencode. (See Tip)

<< Previous | Next >>