gutenberg / wordpress rest api parent page menu bug

[elr0berto]

Describe the bug
Gutenberg and wordpress fails to render the parent page dropdown correctly when there are more than 100 pages and the pages have various menu_order values set.

The problem is that gutenberg calls the wordpress rest api like this, getting 100 items at a time.

http://server/wp-json/wp/v2/pages?per_page=100&exclude=890&parent_exclude=890&orderby=menu_order&order=asc&context=edit&_locale=user
http://server/wp-json/wp/v2/pages?per_page=100&exclude%5B0%5D=890&parent_exclude%5B0%5D=890&orderby=menu_order&order=asc&context=edit&_locale=user&page=2

This results in the following 2 sql queries:
SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts WHERE 1=1 AND wp_posts.ID NOT IN (890) AND wp_posts.post_parent NOT IN (890) AND wp_posts.post_type = 'page' AND ((wp_posts.post_status = 'publish')) ORDER BY wp_posts.menu_order ASC LIMIT 0, 100
SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts WHERE 1=1 AND wp_posts.ID NOT IN (890) AND wp_posts.post_parent NOT IN (890) AND wp_posts.post_type = 'page' AND ((wp_posts.post_status = 'publish')) ORDER BY wp_posts.menu_order ASC LIMIT 100, 100

When ordering on a non unique field like menu_order you need to also add a second unique ordering field like ID ,, See https://bugs.mysql.com/bug.php?id=72076 See the answer from Tor Didriksen.

This is very critical bug because it means that if the current pages parent is missing in the parent page dropdown and you click update it means that the menu order for that page will be reset and this means i cant use gutenberg.

To Reproduce
Steps to reproduce the behavior:

1. Create around 200 pages.
2. Set menu_order != on some of the pages.
3. edit any of the pages.
4. the parent page dropdown is missing pages

Expected behavior
the parent page dropdown should contain all pages except the current page and current page children

Desktop (please complete the following information):

• OS: linux, windows
• any Browser

Additional context

[elr0berto]

This is a bug in wordpress rest-api. triggered by gutenberg.

https://core.trac.wordpress.org/ticket/46294

[elr0berto]

This is serious bug with easy fix.
This makes Gutenberg unusable for anyone with over 100 pages.