WordPressで汎用的にページ(page)を処理するユーティリティークラスです。

test-wp-utils-page.php

<?php
/**
 * InfoTown_Utils_Pagesテスト
 *
 * @package   InfoTown
 * @author    Hiroshi Sawai <info@info-town.jp>
 * @copyright Hiroshi Sawai
 */
class InfoTown_Utils_Pages_Test extends WP_UnitTestCase {

	public static function setUpBeforeClass() {
		parent::setUpBeforeClass();
		require_once( dirname( dirname( dirname( __FILE__ ) ) ) . '/inc/utils/class.pages.php' );
	}

	/**
	 * @group page
	 */
	public function test_get_page_link_by_slug() {
		$expected = [];
		$post_1st = $this->factory->post->create_and_get( [
			'post_name'  => '1st',
			'post_title' => '1st page',
			'post_type'  => 'page',
		] );
		array_push($expected, $post_1st);
		$post_2nd = $this->factory->post->create_and_get( [
			'post_name'   => '2nd',
			'post_title'  => '2nd page',
			'post_type'   => 'page',
			'post_parent' => $post_1st->ID,
		] );
		array_push($expected, $post_2nd);
		$post_3rd = $this->factory->post->create_and_get( [
			'post_name'   => '3rd',
			'post_title'  => '3rd page',
			'post_type'   => 'page',
			'post_parent' => $post_2nd->ID,
		] );
		array_push($expected, $post_3rd);
		$post_4th = $this->factory->post->create_and_get( [
			'post_name'   => '4th',
			'post_title'  => '4th page',
			'post_type'   => 'page',
			'post_parent' => $post_3rd->ID,
		] );
		$actual = InfoTown_Utils_Pages::get_page_link_by_slug($post_4th->post_name);
		$this->assertNotEmpty($actual);
	}
	/**
	 * @group page
	 */
	public function test_is_page_children() {
		$expected = [];
		$post_1st = $this->factory->post->create_and_get( [
			'post_name'  => '1st',
			'post_title' => '1st page',
			'post_type'  => 'page',
		] );
		array_push($expected, $post_1st);
		$post_2nd = $this->factory->post->create_and_get( [
			'post_name'   => '2nd',
			'post_title'  => '2nd page',
			'post_type'   => 'page',
			'post_parent' => $post_1st->ID,
		] );
		array_push($expected, $post_2nd);
		$post_3rd = $this->factory->post->create_and_get( [
			'post_name'   => '3rd',
			'post_title'  => '3rd page',
			'post_type'   => 'page',
			'post_parent' => $post_2nd->ID,
		] );
		array_push($expected, $post_3rd);
		$post_4th = $this->factory->post->create_and_get( [
			'post_name'   => '4th',
			'post_title'  => '4th page',
			'post_type'   => 'page',
			'post_parent' => $post_3rd->ID,
		] );
		$actual = InfoTown_Utils_Pages::is_page_children($post_3rd->ID, $post_1st->ID);
		$this->assertTrue($actual);
		$actual = InfoTown_Utils_Pages::is_page_children($post_2nd->ID, $post_3rd->ID);
		$this->assertFalse($actual);
	}
}

wp-class-utls-page.php

<?php
/**
 * ページ処理
 *
 * @package    InfoTown
 * @subpackage Utils
 * @author     Hiroshi Sawai <info@info-town.jp>
 * @copyright  Hiroshi Sawai
 */
class InfoTown_Utils_Pages {
	/**
	 * 固定ページスラッグからパーマリンク取得
	 *
	 * @param string $slug スタッグです。
	 *
	 * @link https://firegoby.jp/archives/4285
	 *
	 * @return mixed(string | boolean) 引数で指定したスラッグのパーマリングです。
	 */
	public static function get_page_link_by_slug( $slug ) {
		if ( empty( $slug ) ) {
			return false;
		}
		$page = get_posts( [
			'post_type' => 'page',
			'name'      => $slug,
		] );
		if ( 1 !== count( $page ) ) {
			return false;
		}

		return get_page_link( $page[0]->ID );
	}

	/**
	 * 固定ページスラッグからページID取得
	 *
	 * @param string $slug スタッグです。
	 *
	 * @link https://firegoby.jp/archives/4285
	 *
	 * @return mixed(string | boolean) 引数で指定したスラッグのパーマリングです。
	 */
	public static function get_page_id_by_slug( $slug ) {
		if ( empty( $slug ) ) {
			return false;
		}
		$page = get_posts( [
			'post_type' => 'page',
			'name'      => $slug,
		] );
		if ( 1 !== count( $page ) ) {
			return false;
		}

		return $page[0]->ID;
	}

	/**
	 * 子孫ページか検証
	 *
	 * 引数で与えられたページが子孫ページか検証します。
	 *
	 * @param integer $page_id   判定対象の固定ページIDです。
	 * @param integer $parent_id 親ページのIDです。
	 *
	 * @return boolean 子ページのときはtrue, そうでないときはfalseをかえします。
	 */
	public static function is_page_children( $page_id, $parent_id ) {
		$my_wp_query  = new WP_Query();
		$all_wp_pages = $my_wp_query->query( [
			'post_type' => 'page',
			'nopaging'  => 'true',
		] );
		$children     = get_page_children( $parent_id, $all_wp_pages );
		foreach ( $children as $child ) {
			if ( $page_id === $child->ID ) {
				return true;
			}
		}

		return false;
	}
}