I have this function to get the meta keys for all the post types.

 public function pgggo_custom_post_type_keylist()
        {
            //gets the list of post types 
            $pgggo_custompostype_array = $this->pgggo_list_of_posttypes();

            $pgggo_getposts            = array();

            foreach ($pgggo_custompostype_array as $value) {
                $args = array(
                    'numberposts' => 1,
                    'post_type'   => $value,
                );
                if (!empty(get_posts($args)[0]->ID)) {
                    $pgggo_getposts[] = get_posts($args)[0]->ID;
                }

            }
            $new_array = array();
            foreach ($pgggo_getposts as $value) {
                $new_array[] = get_post_custom($value);
            }

            $result = array();
            foreach ($new_array as $sub) {
                $result = array_merge($result, $sub);
            }
            $result     = array_keys($result);
            $result     = array_unique($result);
            $result     = array_combine($result, $result);
            $result[''] = 'NONE';
            return $result;
        }

Though it works fine it results in high database queries and duplicates queries. Is there any method to improve this or alternative solutions?

I have this function to get the meta keys for all the post types.

 public function pgggo_custom_post_type_keylist()
        {
            //gets the list of post types 
            $pgggo_custompostype_array = $this->pgggo_list_of_posttypes();

            $pgggo_getposts            = array();

            foreach ($pgggo_custompostype_array as $value) {
                $args = array(
                    'numberposts' => 1,
                    'post_type'   => $value,
                );
                if (!empty(get_posts($args)[0]->ID)) {
                    $pgggo_getposts[] = get_posts($args)[0]->ID;
                }

            }
            $new_array = array();
            foreach ($pgggo_getposts as $value) {
                $new_array[] = get_post_custom($value);
            }

            $result = array();
            foreach ($new_array as $sub) {
                $result = array_merge($result, $sub);
            }
            $result     = array_keys($result);
            $result     = array_unique($result);
            $result     = array_combine($result, $result);
            $result[''] = 'NONE';
            return $result;
        }

Though it works fine it results in high database queries and duplicates queries. Is there any method to improve this or alternative solutions?

• wp-query
• database
• query
• get-posts

• 1 Can't you just query the postmeta table directly and use DISTINCT in the in the SQL? It might help if you explain why you are doing this. – Ted Stresen-Reuter Commented Sep 10, 2019 at 21:55

1 Answer 1

As mentioned in the comments you can query the postmeta table directly:

public function get_metadata_keys(){
    global $wpdb;

    $meta_query = $wpdb->get_results(
        "
        SELECT DISTINCT meta_key
        FROM {$wpdb->postmeta}
        "
    , ARRAY_A );

    $meta_keys = wp_list_pluck( $meta_query, 'meta_key' );
    return $meta_keys;
}

This will return the list of all meta_keys associated to any post.