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Lesson 15: Query strings, part I |
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Lesson 15: Query strings, part I
Summary:
Learn to use query strings to pass information between ASP pages.
View the demo to see the result.
Intro:
Often when you build web applications you need to
pass information from one page to another. This can
be done in four ways: cookies, session variables,
forms and query strings.
Query strings are a way to pack information into a link, and then
retrieve that information on the page that was linked to.
Let me show you: A regular URL to a page is like this page.asp.
The URL with a query string might look like this page.asp?id=1.
See the difference? We have added ?id=1 to the URL. But how
do we retrieve such information in the next page. It's pretty easy, just use:
<%
Query_ID = Request.QueryString("ID")
%>
The value is now stored in our variable Query_ID.
And if the url to the page had the query string ?id=1, then
Query_ID is now 1. Let's try it out.
Let's take apart the code for this little demo.
First we have the link page:
<HTML>
<BODY>
<B>Click one of the links below:</B><BR>
<A HREF="page.asp?link=1">Link 1</A><BR>
<A HREF="page.asp?link=2">Link 2</A><BR>
<A HREF="page.asp?link=3">Link 3</A><BR>
<A HREF="page.asp?link=4">Link 4</A><BR>
<A HREF="page.asp?link=5">Link 5</A>
</BODY>
</HTML>
As you see so have I used a query string in every URL to mark which
linked is being clicked. Let's see the code behind page1.asp:
<HTML>
<BODY>
You clicked link number <%=Request.QueryString("link")%>!<BR><BR>
<A HREF="default.asp">Try again</A>
</BODY>
</HTML>
Here we retrive the query string, and then outputs it directly, telling
the user which link he have clicked.
Encoding a query string:
When you use query strings, you must URL-encode it before you
pass it. All spaces must be converted to
addition signs etc. If you don't URL-encode it, you may get some very
strange results. To URL-encode something with ASP is very easy, just
use Server.URLEncode(). Let's try it
on this sentence: "Some info that I need.":
<A HREF="page.asp?sentence=<%=Server.URLEncode("Some info that I need.")%>">Click here!</A>
After URL encoding, the sentence will look like this: Some+info+that+I+need%2E
You don't have to URL-encode the name of neither the query string nor the equal
sign, just the value.
Decoding a query string:
Decoding a query string couldn't be easier: ASP does it
for you! So the sentence from our last example would be
displayed normally if we on the next page used:
<%=Request.QueryString("Sentence")%>
More query strings
Learn to use multiple parameters and multiple values, dumping
the content of the QueryString collection and when not to
use query strings: Lesson 16.
Where to go next:
Check out the other lessons about parsing values between ASP pages:
Lesson 8: Cookies and Lesson 13: Forms.
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