CFLib.org – Common Function Library Project

Description:
Changes the value of a variable in a query string. By default it will use cgi.query_string, but you can pass in an optional third argument to act as the query string. This function is handy when you have, for instance, a table with column headers that allow you to sort by different variables -- in that case you could preserve the entire query string and replace only the sort variable.

Return Values:
Returns a string.

Example:

<cfset qs = "foo=1&goo=2&name=nathan">
<cfset newqs = QueryStringChangeVar("name","ray",qs)>
<cfoutput>New QueryString: #newqs#</cfoutput>

Parameters:

Full UDF Source:

<cfscript>
/**
 * Changes a var in a query string.
 * 
 * @param name 	 The name of the name/value pair you want to modify. (Required)
 * @param value 	 The new value for the name/value pair you want to modify. (Required)
 * @param qs 	 Query string to modify. Defaults to CGI.QUERY_STRING. (Optional)
 * @return Returns a string. 
 * @author Nathan Dintenfass (&#110;&#97;&#116;&#104;&#97;&#110;&#64;&#99;&#104;&#97;&#110;&#103;&#101;&#109;&#101;&#100;&#105;&#97;&#46;&#99;&#111;&#109;) 
 * @version 2, September 5, 2002 
 */
function QueryStringChangeVar(variable,value){
	//var to hold the final string
	var string = "";
	//vars for use in the loop, so we don't have to evaluate lists and arrays more than once
	var ii = 1;
	var thisVar = "";
	var thisIndex = "";
	var array = "";
	var changedIt = 0;
	//if there is a third argument, use that as the query string, otherwise default to cgi.query_string
	var qs = cgi.query_string;
	if(arrayLen(arguments) GT 2)
		qs = arguments[3];

	//put the query string into an array for easier looping
	array = listToArray(qs,"&");
	//now, loop over the array and rebuild the string
	for(ii = 1; ii lte arrayLen(array); ii = ii + 1){
		thisIndex = array[ii];
		thisVar = listFirst(thisIndex,"=");
		//if this is the var, edit it to the value, otherwise, just append
		if(thisVar is variable){
			string = listAppend(string,thisVar & "=" & value,"&");
			changedIt = 1;
		}
		else{
			string = listAppend(string,thisIndex,"&");
		}
	}
	//if it was not changed, add it!
	if(NOT changedIt)
		string = listAppend(string,variable & "=" & value,"&");
	//return the string
	return string;
}
</cfscript>