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Question

I'm trying to filter the 'All posts' admin screen in order to retrieve posts with unique categories. By now, I've manage to set a $_GET key in the url with prase_query hook:

add_filter( 'parse_query', 'lxa_admin_posts_filter' );
   function lxa_admin_posts_filter( $query ) {
     global $pagenow;
        if ( is_admin() && $pagenow=='edit.php' && isset($_GET['category_only']) && $_GET['category_only'] != '') {
        $query->query_vars['meta_key'] = $_GET['category_only'];
    }
}

Later on, using restrict_manage_posts hook, I've created a dropdown containing all my post's category:

function lxa_admin_posts_filter_restrict_manage_posts() {
global $wpdb;

$categories = get_categories( array(
    'taxonomy' => 'category',
    'orderby' => 'name',
    'parent'  => 0,
    'hierarchical' => true,
) );

?>
<select name="category_only">
<option value=""><?php _e('Filter By Category Only', 'baapf'); ?></option>
<?php   foreach ( $categories as $category ) {
    echo  '<option value= "' . $category -> term_id . '" > ' . $category -> name . '</option>';

}

?>
</select>


<?php }

It is possible using this 'category_only' key to alter the loop in order to retrieve post with only one category?

Thank you

Answer 1

I suggest using this code:

/**
 * Display a custom taxonomy dropdown in admin
 * @author Mike Hemberger
 * @link http://thestizmedia.com/custom-post-type-filter-admin-custom-taxonomy/
 */
add_action('restrict_manage_posts', 'tsm_filter_post_type_by_taxonomy');
function tsm_filter_post_type_by_taxonomy() {
    global $typenow;
    $post_type = 'lessons_cpt'; // change to your post type
    $taxonomy  = 'chapters'; // change to your taxonomy
    if ($typenow == $post_type) {
        $selected      = isset($_GET[$taxonomy]) ? $_GET[$taxonomy] : '';
        $info_taxonomy = get_taxonomy($taxonomy);
        wp_dropdown_categories(array(
            'show_option_all' => __("Show All {$info_taxonomy->label}"),
            'taxonomy'        => $taxonomy,
            'name'            => $taxonomy,
            'orderby'         => 'name',
            'selected'        => $selected,
            'show_count'      => true,
            'hide_empty'      => true,
        ));
    };
}
/**
 * Filter posts by taxonomy in admin
 * @author  Mike Hemberger
 * @link http://thestizmedia.com/custom-post-type-filter-admin-custom-taxonomy/
 */
add_filter('parse_query', 'tsm_convert_id_to_term_in_query_videos');
function tsm_convert_id_to_term_in_query_videos($query) {
    global $pagenow;
    $post_type = 'lessons_cpt'; // change to your post type
    $taxonomy  = 'chapters'; // change to your taxonomy
    $q_vars    = &$query->query_vars;
    if ( $pagenow == 'edit.php' && isset($q_vars['post_type']) && $q_vars['post_type'] == $post_type && isset($q_vars[$taxonomy]) && is_numeric($q_vars[$taxonomy]) && $q_vars[$taxonomy] != 0 ) {

    $term = get_term_by('id', $q_vars[$taxonomy], $taxonomy);
        $q_vars[$taxonomy] = $term->slug;
    }
}

You just need to change CPT and Taxonomy. I have used in a recent project and it works great.

Source: http://thestizmedia.com/custom-post-type-filter-admin-custom-taxonomy/