select onchange add get variable to url - php

Question

I am using multiple select elements on a page. This page's url is something like this: "index.php?s=foo".
Now I want that changing my select boxes will alter my URL and refresh page, this just works partly :(
Here is the example:
<form action="'.$_SERVER['REQUEST_URI'].'" method="GET">
<select name="this" onchange="this.form.submit()">
<option value="1">Value 1</option>
<option value="2">Value 2</option>
<option value="3">Value 3</option>
</select>
</form>
So if I change my selection the url will swap to "index.php?this=1", but I would like to hold the previous _GET Parameters, so change would occur to "index.php?s=foo&this=1".
Any chance I would get that?
Thanks very much for your help.
Best Regards

Answer 1

Using REQUEST_URI does not include your current GET parameters. You will need the function in this gist to transform all parameters into input fields: https://gist.github.com/eric1234/5802030 .
<form action="<?php echo $_SERVER['SCRIPT_NAME']; ?>" method="get">
<?php array_to_input($_GET); ?>
<select name="this" onchange="this.form.submit()">
<option value="1">Value 1</option>
<option value="2">Value 2</option>
<option value="3">Value 3</option>
</select>
</form>
CAUTION: array_to_input can introduce XSS vulnerabilities. Please escape contents of the $_GET variable so this cannot happen.

Answer 2

You could add each query string item as a hidden field which will be added to the query string when the form is submitted. Be sure to do some sanitizing on these things to make them safe.
if(!empty($_GET))
{
foreach($_GET AS $k => $v)
{
echo '<input type="hidden" name="'.$k.'" value="'.$v.'">';
}
}
The form action can then be hard coded to something like the file name or $_SERVER['SCRIPT_NAME']. Not $_SERVER['PHP_SELF'] - as pointed out by comment below.
edit : posted answer before I was finished. :(

Answer 3

The simple answer is instead of this:
<form action="'.$_SERVER['REQUEST_URI'].'" method="GET">
Do the action like this:
<form action="<?php echo $_SERVER['REQUEST_URI'].'?'.$_SERVER['QUERY_STRING']; ?>" method="GET">
Which will include the current $_GET values in your form's action/url and by extension be present when the form is submitted. Basically that is the way forms are designed in general to handle submission to a page with query parameters, ie. the default way it works.
Just a note but I think the way you have it now you might get this for your action/url
"http://'.$_SERVER['REQUEST_URI'].'"
It's just a guess, but it looks like the form is html, and the php will just print and not be executed as code ( without php tags ). Probably just an over-site in the example code. But, I would expect this with the format you have:
echo '<form action="'.$_SERVER['REQUEST_URI'].'" method="GET">';
Cheers!