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How to use query_vars filter in WordPress

Sandeep Kumar Mishra
Sandeep Kumar Mishra
July 12, 2022
5 minutes read

query_vars filter

Allows (publicly allowed) query vars to be added, removed, or changed prior to executing the query. Needed to allow custom rewrite rules using your own arguments to work, or any other custom query variables you want to be publicly available.

To use query_vars filter, first you have to register it using add_filter. You can write this code into functions.php of your activated theme or in a custom WordPress Plugin.

We at Flipper Code, always prefer to create a custom WordPress Plugin while using hooks so nothing breaks when you update your WordPress Theme in the future.

In the below live example, we have defined a function modify_query_vars_defaults which takes 1 parameters and we registered using add_filter. The first parameter query_vars is name of the hook, The second parameter modify_query_vars_defaults is name of the function which need to be called, third parameter is the priority of calling the hook if same hook is used multiple times and the last parameter is the number of arguments (if any) to be passed in the registered function.

Sometime, you have to remove a registered hook so you can use remove_filter to remove query_vars filter.

Parameters

    Below the 1 parameter is required to use this hook.

  • $public_query_vars : (string[]) The array of allowed query variable names.

Live Example

function myplugin_query_vars( $qvars ) {
    $qvars[] = 'custom_query_var';
    return $qvars;
}
add_filter( 'query_vars', 'myplugin_query_vars' );

Below is an example how you can use this hook.

                        function modify_query_vars_defaults($public_query_vars) { 
   
                            // Update the $public_query_vars variable according to your website requirements and return this variable. You can modify the $public_query_vars variable conditionally too if you want.

                            return $public_query_vars; 
                        }
                        // add the filter
                        add_filter( "query_vars", "modify_query_vars_defaults", 10, 1 );

To remove a hook callback, use the example below.

remove_filter( "query_vars", "modify_query_vars_defaults", 10, 1 );

Please make sure provide the same callback function name, priority and number of arguments while removing the hook callback.

Flipper Code is a Premium WordPress Plugins development company and integrating new functionalites into WordPress sites in form of custom WordPress Plugins since 2012. If you’re having any trouble using this hook, please contact our WordPress Development Team and we’d be happy to assist you.

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