WP_Tax_Query::transform_query( array $query, string $resulting_field )

596	public function transform_query( &$query, $resulting_field ) {597		if ( empty( $query['terms'] ) ) {598			return;599		}600 601		if ( $query['field'] === $resulting_field ) {602			return;603		}604 605		$resulting_field = sanitize_key( $resulting_field );606 607		// Empty 'terms' always results in a null transformation.608		$terms = array_filter( $query['terms'] );609		if ( empty( $terms ) ) {610			$query['terms'] = array();611			$query['field'] = $resulting_field;612			return;613		}614 615		$args = array(616			'get'                    => 'all',617			'number'                 => 0,618			'taxonomy'               => $query['taxonomy'],619			'update_term_meta_cache' => false,620			'orderby'                => 'none',621		);622 623		// Term query parameter name depends on the 'field' being searched on.624		switch ( $query['field'] ) {625			case 'slug':626				$args['slug'] = $terms;627				break;628			case 'name':629				$args['name'] = $terms;630				break;631			case 'term_taxonomy_id':632				$args['term_taxonomy_id'] = $terms;633				break;634			default:635				$args['include'] = wp_parse_id_list( $terms );636				break;637		}638 639		if ( ! is_taxonomy_hierarchical( $query['taxonomy'] ) ) {640			$args['number'] = count( $terms );641		}642 643		$term_query = new WP_Term_Query();644		$term_list  = $term_query->query( $args );645 646		if ( is_wp_error( $term_list ) ) {647			$query = $term_list;648			return;649		}650 651		if ( 'AND' === $query['operator'] && count( $term_list ) < count( $query['terms'] ) ) {652			$query = new WP_Error( 'inexistent_terms', __( 'Inexistent terms.' ) );653			return;654		}655 656		$query['terms'] = wp_list_pluck( $term_list, $resulting_field );657		$query['field'] = $resulting_field;658	}