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_get_term_hierarchy()

_get_term_hierarchy( string $taxonomy ): array

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This function’s access is marked private. This means it is not intended for use by plugin or theme developers, only in other core functions. It is listed here for completeness.

Retrieves children of taxonomy as term IDs.

Parameters

$taxonomystringrequired
Taxonomy name.

Return

array Empty if $taxonomy isn’t hierarchical or returns children as term IDs.

Source

function _get_term_hierarchy( $taxonomy ) {
	if ( ! is_taxonomy_hierarchical( $taxonomy ) ) {
		return array();
	}
	$children = get_option( "{$taxonomy}_children" );

	if ( is_array( $children ) ) {
		return $children;
	}
	$children = array();
	$terms    = get_terms(
		array(
			'taxonomy'               => $taxonomy,
			'get'                    => 'all',
			'orderby'                => 'id',
			'fields'                 => 'id=>parent',
			'update_term_meta_cache' => false,
		)
	);
	foreach ( $terms as $term_id => $parent ) {
		if ( $parent > 0 ) {
			$children[ $parent ][] = $term_id;
		}
	}
	update_option( "{$taxonomy}_children", $children );

	return $children;
}

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UsesDescription
get_terms()wp-includes/taxonomy.php

Retrieves the terms in a given taxonomy or list of taxonomies.

is_taxonomy_hierarchical()wp-includes/taxonomy.php

Determines whether the taxonomy object is hierarchical.

update_option()wp-includes/option.php

Updates the value of an option that was already added.

get_option()wp-includes/option.php

Retrieves an option value based on an option name.

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Used byDescription
clean_taxonomy_cache()wp-includes/taxonomy.php

Cleans the caches for a taxonomy.

WP_Term_Query::get_terms()wp-includes/class-wp-term-query.php

Retrieves the query results.

_wp_batch_split_terms()wp-includes/taxonomy.php

Splits a batch of shared taxonomy terms.

WP_Terms_List_Table::display_rows_or_placeholder()wp-admin/includes/class-wp-terms-list-table.php
_get_term_children()wp-includes/taxonomy.php

Gets the subset of $terms that are descendants of $term_id.

_pad_term_counts()wp-includes/taxonomy.php

Adds count of children to parent count.

get_term_children()wp-includes/taxonomy.php

Merges all term children into a single array of their IDs.

_wp_menu_item_classes_by_context()wp-includes/nav-menu-template.php

Adds the class property classes for the current context, if applicable.

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Changelog

VersionDescription
2.3.0Introduced.

User Contributed Notes

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    Codex
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       /** The taxonomy we want to parse */
   $taxonomy = "category";
   /** Get all taxonomy terms */
   $terms = get_terms($taxonomy, array(
           "orderby"    => "count",
           "hide_empty" => false
       )
   );
   /** Get terms that have children */
   $hierarchy = _get_term_hierarchy($taxonomy);
       /** Loop through every term */
       foreach($terms as $term) {
       //Skip term if it has children
       if($term->parent) {
         continue;
       }
         echo $term->name;
       /** If the term has children... */
         if($hierarchy[$term->term_id]) {
       /** display them */
       foreach($hierarchy[$term->term_id] as $child) {
       /** Get the term object by its ID */
       $child = get_term($child, "category_list");
            echo '--'.$child->name;
           }
        }
     }

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