HACK! Modification to mod.search.php to support "category='not ...'" in ExpressionEngine's advance search (start at line 1014). USE AT YOUR OWN RISK!

gistfile1.txt

/** ----------------------------------------------
/**  Limit query to a specific category
/** ----------------------------------------------*/
		
// Check for different sets of category IDs, checking the parameters
// first, then the $_POST
$exclude_cat = false;
		
if (isset($this->_meta['category']) AND $this->_meta['category'] != '' AND ! is_array($this->_meta['category']))
{
	if(strpos($this->_meta['category'], "not ") > -1) {
		$exclude_cat = true;
		$this->_meta['category'] = str_replace("not ", "", $this->_meta['category']);
	}
	$this->_meta['category'] = explode('|', $this->_meta['category']);
}
else if (
	( ! isset($this->_meta['category']) OR $this->_meta['category'] == '') AND
	(isset($_POST['cat_id']) AND is_array($_POST['cat_id']))
)
{
	$this->_meta['category'] = $_POST['cat_id'];
}
else
{
	$this->_meta['category'] = '';
} 



if (is_array($this->_meta['category']))
{		
	$temp = '';
	
	if($exclude_cat) {
		foreach ($this->_meta['category'] as $val)
		{
			if ($val != 'all' AND $val != '')
			{
				$temp .= " exp_categories.cat_id != '".$this->EE->db->escape_str($val)."' AND";
			}
		} 

		if ($temp != '')
		{
			$temp = substr($temp, 0, -3);

			$sql .= ' AND ('.$temp.' OR exp_categories.cat_id IS NULL) ';
		}
	} else {
		foreach ($this->_meta['category'] as $val)
		{
			if ($val != 'all' AND $val != '')
			{
				$temp .= " exp_categories.cat_id = '".$this->EE->db->escape_str($val)."' OR";
			}
		} 

		if ($temp != '')
		{
			$temp = substr($temp, 0, -2);

			$sql .= ' AND ('.$temp.') ';
		}
	}
	
}

/** ----------------------------------------------
/**  Are there results?
/** ----------------------------------------------*/

This is an UNOFFICIAL, UNSUPPORTED HACK to mod.search.php in ExpressionEngine. USE AT YOUR OWN RISK! I'm not affiliated with EllisLabs, just a dev who needed the ability to exclude categories in search (and still search for uncategorized entries) and felt it was ridiculous to pay for a $99 3rd party module for this basic functionality.