I am using Post Grid plugin to display a catalog for a record company using custom post types and taxonomies. They want to be able to filter by artist and genre on the front end, and I have looked at the Post Grid documentation to find a shortcode php file that you can use to add this to a widget in my sidebar. I’ve gotten most everything to work, it shows up in the sidebar widget using the shortcode i generated, the 2 dropdowns are there for artist and genre, and they correctly populate in the dropdown based on the current taxonomies present. I can NOT for the life of me figure out how to make it actually filter the data after pressing ‘submit’ and it just shows everything unfiltered. Here is the code I am using.

<?php
add_shortcode('post_grid_filter_form','post_grid_filter_form');

if ( ! defined('ABSPATH')) exit;  // if direct access

function post_grid_filter_form($args){

    $page_url = '';

    ?>
    <div class="post-grid-filter">
        <form action="#<?php //echo $page_url; ?>" method="get">
            <?php
            do_action('post_grid_filter', $args);
            ?>
            <div class="field-wrap submit">
                <div class="field-input">
                    <?php wp_nonce_field( 'nonce_post_grid_filter' ); ?>
                    <input type="submit" class=""  placeholder="" value="Submit">

                </div>
            </div>
        </form>
    </div>
    <?php
}


//FILTER BY ARTIST

add_action('post_grid_filter', 'post_grid_filter_artist_field');

function post_grid_filter_artist_field($args){

    $terms = get_terms( array(
        'taxonomy' => 'artist',
        'hide_empty' => false,
    ) );

    //var_dump($terms);
    $pgs_artist = isset($_GET['pgs_artist']) ? sanitize_text_field($_GET['pgs_artist']) : '';

    ?>

    <div class="field-wrap">
        <div class="field-label">Filter by Artist</div>
        <div class="field-input">
            <select name="pgs_artist">
                <option><?php echo __('Choose Artist', ''); ?></option>
                <?php

                if(!empty($terms))
                foreach ($terms as $term){

                    $term_id = isset($term->term_id) ? $term->term_id : '';
                    $term_name = isset($term->name) ? $term->name : '';

                    ?>
                    <option <?php echo selected($term_id, $pgs_artist)?> value="<?php echo $term_id; ?>"><?php echo $term_name; ?></option>
                    <?php

                }

                ?>
            </select>
        </div>
    </div>

    <?php

}


//FILTER BY GENRE

add_action('post_grid_filter', 'post_grid_filter_genre_field');

function post_grid_filter_genre_field($args){

    $terms = get_terms( array(
        'taxonomy' => 'genre',
        'hide_empty' => false,
    ) );

    //var_dump($terms);
    $pgs_artist = isset($_GET['pgs_genre']) ? sanitize_text_field($_GET['pgs_genre']) : '';

    ?>

    <div class="field-wrap">
        <div class="field-label">Filter by Genre</div>
        <div class="field-input">
            <select name="pgs_genre">
                <option><?php echo __('Choose Genre', ''); ?></option>
                <?php

                if(!empty($terms))
                foreach ($terms as $term){

                    $term_id = isset($term->term_id) ? $term->term_id : '';
                    $term_name = isset($term->name) ? $term->name : '';

                    ?>
                    <option <?php echo selected($term_id, $pgs_artist)?> value="<?php echo $term_id; ?>"><?php echo $term_name; ?></option>
                    <?php

                }

                ?>
            </select>
        </div>
    </div>

    <?php

}



// Process form data and post query

function post_grid_query_custom_search($query_args, $args){

    $current_post_id = get_the_ID();

    $pgs_artist = isset($_GET['pgs_artist']) ? sanitize_text_field($_GET['pgs_artist']) : '';
    $pgs_genre = isset($_GET['pgs_genre']) ? sanitize_text_field($_GET['pgs_genre']) : '';

    $query_args['s'] = $pgs_artist;

    return $query_args;
}

add_filter('post_grid_query_args','post_grid_query_custom_search', 90, 2);