我正在自定义帖子类型“book”列表页面上添加一个过滤器，以便于搜索。我已经找到了相关的代码，除了过滤器不仅出现在“book”列表页上，而且还出现在其他列表页上，例如post列表页上，其他一切都很好。我已经检查了代码，但仍然不清楚。

<?php
add_action( \'restrict_manage_posts\', \'book_genre_filter_page\' );

function book_genre_filter_page(){
$type = \'book\';

if (\'book\' == $type){

    $values = array(
        \'Science Fiction\' => \'sf\', 
        \'Autobiography\' => \'ab\',
        \'Thriller\' => \'t\',
    );
    ?>
    <select name="genre">
    <option value=""><?php _e(\'All genres\', \'book_genre\'); ?></option>
    <?php
        $current_v = isset($_GET[\'genre\'])? $_GET[\'genre\']:\'\';
        foreach ($values as $label => $value) {
            printf
                (
                    \'<option value="%s"%s>%s</option>\',
                    $value,
                    $value == $current_v? \' selected="selected"\':\'\',
                    $label
                );
            }
    ?>
    </select>
    <?php
}
}


add_filter( \'parse_query\', \'book_genre_filter\' );

function book_genre_filter( $query ){
global $pagenow;
$type = $query->query[\'post_type\'];
    $target = \'book\';

    if ( $type == $target ) {
        if ( $pagenow ==\'edit.php\' && isset($_GET[\'genre\']) && $_GET[\'genre\'] != \'\') {
                $query->query_vars[\'meta_key\'] = \'genre\';
                $query->query_vars[\'meta_value\'] = $_GET[\'genre\']; 
        }
    }
}