Source

File: wp-includes/taxonomy.php

function wp_delete_term( $term, $taxonomy, $args = array() ) {
	global $wpdb;

	$term = (int) $term;

	$ids = term_exists( $term, $taxonomy );
	if ( ! $ids ) {
		return false;
	}
	if ( is_wp_error( $ids ) ) {
		return $ids;
	}

	$tt_id = $ids['term_taxonomy_id'];

	$defaults = array();

	if ( 'category' === $taxonomy ) {
		$defaults['default'] = (int) get_option( 'default_category' );
		if ( $defaults['default'] === $term ) {
			return 0; // Don't delete the default category.
		}
	}

	// Don't delete the default custom taxonomy term.
	$taxonomy_object = get_taxonomy( $taxonomy );
	if ( ! empty( $taxonomy_object->default_term ) ) {
		$defaults['default'] = (int) get_option( 'default_term_' . $taxonomy );
		if ( $defaults['default'] === $term ) {
			return 0;
		}
	}

	$args = wp_parse_args( $args, $defaults );

	if ( isset( $args['default'] ) ) {
		$default = (int) $args['default'];
		if ( ! term_exists( $default, $taxonomy ) ) {
			unset( $default );
		}
	}

	if ( isset( $args['force_default'] ) ) {
		$force_default = $args['force_default'];
	}

	/**
	 * Fires when deleting a term, before any modifications are made to posts or terms.
	 *
	 * @since 4.1.0
	 *
	 * @param int    $term     Term ID.
	 * @param string $taxonomy Taxonomy Name.
	 */
	do_action( 'pre_delete_term', $term, $taxonomy );

	// Update children to point to new parent.
	if ( is_taxonomy_hierarchical( $taxonomy ) ) {
		$term_obj = get_term( $term, $taxonomy );
		if ( is_wp_error( $term_obj ) ) {
			return $term_obj;
		}
		$parent = $term_obj->parent;

		$edit_ids    = $wpdb->get_results( "SELECT term_id, term_taxonomy_id FROM $wpdb->term_taxonomy WHERE `parent` = " . (int) $term_obj->term_id );
		$edit_tt_ids = wp_list_pluck( $edit_ids, 'term_taxonomy_id' );

		/**
		 * Fires immediately before a term to delete's children are reassigned a parent.
		 *
		 * @since 2.9.0
		 *
		 * @param array $edit_tt_ids An array of term taxonomy IDs for the given term.
		 */
		do_action( 'edit_term_taxonomies', $edit_tt_ids );

		$wpdb->update( $wpdb->term_taxonomy, compact( 'parent' ), array( 'parent' => $term_obj->term_id ) + compact( 'taxonomy' ) );

		// Clean the cache for all child terms.
		$edit_term_ids = wp_list_pluck( $edit_ids, 'term_id' );
		clean_term_cache( $edit_term_ids, $taxonomy );

		/**
		 * Fires immediately after a term to delete's children are reassigned a parent.
		 *
		 * @since 2.9.0
		 *
		 * @param array $edit_tt_ids An array of term taxonomy IDs for the given term.
		 */
		do_action( 'edited_term_taxonomies', $edit_tt_ids );
	}

	// Get the term before deleting it or its term relationships so we can pass to actions below.
	$deleted_term = get_term( $term, $taxonomy );

	$object_ids = (array) $wpdb->get_col( $wpdb->prepare( "SELECT object_id FROM $wpdb->term_relationships WHERE term_taxonomy_id = %d", $tt_id ) );

	foreach ( $object_ids as $object_id ) {
		$terms = wp_get_object_terms(
			$object_id,
			$taxonomy,
			array(
				'fields'  => 'ids',
				'orderby' => 'none',
			)
		);
		if ( 1 === count( $terms ) && isset( $default ) ) {
			$terms = array( $default );
		} else {
			$terms = array_diff( $terms, array( $term ) );
			if ( isset( $default ) && isset( $force_default ) && $force_default ) {
				$terms = array_merge( $terms, array( $default ) );
			}
		}
		$terms = array_map( 'intval', $terms );
		wp_set_object_terms( $object_id, $terms, $taxonomy );
	}

	// Clean the relationship caches for all object types using this term.
	$tax_object = get_taxonomy( $taxonomy );
	foreach ( $tax_object->object_type as $object_type ) {
		clean_object_term_cache( $object_ids, $object_type );
	}

	$term_meta_ids = $wpdb->get_col( $wpdb->prepare( "SELECT meta_id FROM $wpdb->termmeta WHERE term_id = %d ", $term ) );
	foreach ( $term_meta_ids as $mid ) {
		delete_metadata_by_mid( 'term', $mid );
	}

	/**
	 * Fires immediately before a term taxonomy ID is deleted.
	 *
	 * @since 2.9.0
	 *
	 * @param int $tt_id Term taxonomy ID.
	 */
	do_action( 'delete_term_taxonomy', $tt_id );

	$wpdb->delete( $wpdb->term_taxonomy, array( 'term_taxonomy_id' => $tt_id ) );

	/**
	 * Fires immediately after a term taxonomy ID is deleted.
	 *
	 * @since 2.9.0
	 *
	 * @param int $tt_id Term taxonomy ID.
	 */
	do_action( 'deleted_term_taxonomy', $tt_id );

	// Delete the term if no taxonomies use it.
	if ( ! $wpdb->get_var( $wpdb->prepare( "SELECT COUNT(*) FROM $wpdb->term_taxonomy WHERE term_id = %d", $term ) ) ) {
		$wpdb->delete( $wpdb->terms, array( 'term_id' => $term ) );
	}

	clean_term_cache( $term, $taxonomy );

	/**
	 * Fires after a term is deleted from the database and the cache is cleaned.
	 *
	 * @since 2.5.0
	 * @since 4.5.0 Introduced the `$object_ids` argument.
	 *
	 * @param int     $term         Term ID.
	 * @param int     $tt_id        Term taxonomy ID.
	 * @param string  $taxonomy     Taxonomy slug.
	 * @param mixed   $deleted_term Copy of the already-deleted term, in the form specified
	 *                              by the parent function. WP_Error otherwise.
	 * @param array   $object_ids   List of term object IDs.
	 */
	do_action( 'delete_term', $term, $tt_id, $taxonomy, $deleted_term, $object_ids );

	/**
	 * Fires after a term in a specific taxonomy is deleted.
	 *
	 * The dynamic portion of the hook name, `$taxonomy`, refers to the specific
	 * taxonomy the term belonged to.
	 *
	 * @since 2.3.0
	 * @since 4.5.0 Introduced the `$object_ids` argument.
	 *
	 * @param int     $term         Term ID.
	 * @param int     $tt_id        Term taxonomy ID.
	 * @param mixed   $deleted_term Copy of the already-deleted term, in the form specified
	 *                              by the parent function. WP_Error otherwise.
	 * @param array   $object_ids   List of term object IDs.
	 */
	do_action( "delete_{$taxonomy}", $term, $tt_id, $deleted_term, $object_ids );

	return true;
}