Filtering Children of the “uncategorized” Category out of the Loop?

Question

I have some utility categories that are only used by my theme. To help separate these categories I place them all as children of uncategorized.

How can I make sure that any call to wp_list_categories() excludes the child categories under "uncategorized" cat_id = 1?

I want this to work even if the call wp_list_categories() comes from a third party plugin that I don't control.

Perhaps a filter I can place in functions.php that intercepts any call for the wp_list_categories() function to attach the exlude_tree = '1' to the arguments.

For example, in my own categories plugin widget, I use this...

    <ul>
<?php
    $cat_args['title_li'] = '';
    $cat_args['exclude_tree'] = 1;
    wp_list_categories(apply_filters('widget_categories_args', $cat_args));
?>
    </ul>

Answer 1

Hi @Scott B:

UPDATE FROM PRIOR ANSWER: Due you my evidently poor reading comprehension skills(!) where I missed the requirement to filter out children (Thanks @Adam BlackStrom for calling attention to my oversight) I've modified the code provided.

---

I think you want to use the list_terms_exclusions filter hook. Add this to your plugin (or others needing the same add to the bottom of your theme's functions.php file):

function my_list_terms_exclusions($exclusions,$args) {
  $children = implode(',',get_term_children(1,'category'));
  $children = (empty($children) ? '' : ",$children");
  return $exclusions . " AND (t.term_id NOT IN (1{$children}))";
}

Of course the above will affect all category listings which you might not want so you might need to inspect the values in the $args array or more likely inspect other global state to only add the filter criteria only in the context(s) in which you need it.

If you have specifics we of where you need help limiting please ask a follow up question so we can help.

P.S. Also, I agree with Adam. If possible use a custom taxonomy.

Answer 2

New answer based on OP comments:

There isn't a filter or hook you can use with wp_list_categories, but there is a filter on the get_categories function that it calls.

The get_categories function makes this call:

$taxonomy = apply_filters( 'get_categories_taxonomy', $args['taxonomy'], $args );

The $args variable in this case is an array constructed originally from wp_list_categories and then merged with 'taxonomy' => 'category'. So you should be able to add a filter here to always set exclude_tree='1'.

Just be sure to specify that your function takes two parameters:

function exclude_children($taxonomy, $args) {
    $args['exclude_tree'] => '1';
}

add_filter('get_categories_taxonomy', 'exclude_children', 10, 2);

Answer 3

Here's some code to modify get_terms() to exclude "Uncategorized" and any children:

// modify the term list to exclude "Uncategorized" and any children
function no_uncategorized( $terms, $taxonomies, $args ) {
    global $my_excluded_categories;

    $uncategorized = term_exists( 'Uncategorized', 'category' );

    $my_excluded_categories = get_term_children( $uncategorized['term_id'], 'category' );
    $my_excluded_categories[] = $uncategorized['term_id'];

    $terms = array_filter( $terms, 'no_uncategorized_filter' );

    return $terms;
}

// used by array_filter to exclude anything in the excluded categories
function no_uncategorized_filter( $category ) {
    global $my_excluded_categories;
    return !in_array( $category->term_id, $my_excluded_categories );
}

// only done during template_redirect (the public-facing site)
function do_template_redirect() {
    add_filter( 'get_terms', 'no_uncategorized', 10, 3 );
}
add_action( 'template_redirect', 'do_template_redirect' );

I think the real answer, though, is don't use categories, instead register your own taxonomy. No more hidden categories, just a private taxonomy that isn't picked up by wp_list_categories().