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:

/**
 * 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 (nathan@changemedia.com) 
 * @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;
}