I deleted a column in #__content_frontpage table, run the schema checker and see the problem:

Table 'jos_content_frontpage' does not have column 'featured_down'. (From file 4.0.0-2019-08-20.sql.)

But it's displayed for "Joomla CMS" extension (eid=208) where element is joomla. Is it correct to compare element as com_admin ?

Surprisingly, clicking "Update Structure" helped even on the current beta3 code without patch applied (the column was re-created).

But it's displayed for "Joomla CMS" extension (eid=208) where element is joomla. Is it correct to compare element as com_admin ?

Here it is extension ID 213, which has element = 'com_admin. Maybe the difference is due to your update history? I have used a brand nex installation of current 4.0-dev branch. But you can check it yourself by adding some debug output like in my instructions, extended a bit, e.g. error_log('$i=' . $i . ', $cid=' . $cid . ', $changeSet[\'extension\']->element=' .$changeSet['extension']->element);

deleted a column ....
Surprisingly, clicking "Update Structure" helped even on the current beta3 code without patch applied (the column was re-created).

Well, that is how it shall work and is absolutely unrelated to this PR. The schema changes are done anway, with and without this PR. The only thing what the check for ' com_admin' is good for is to run additional utf8mb4 stuff for the core.

@Denitz You are right, it's weird that in database, the extension record has element = 'joomla'. But could you test as described in the testing instructions, and if in doubt add the additional debug output which I've mentioned in my previous comment? Then you should see it my PR works or not. I think the reason is that the changeset of the core belongs to com_admin and not to joomla files which is used for display.

Just corrected testing instructions, now they are ok.

@Denitz If you add the error_log('$i=' . $i . ', $cid=' . $cid . ', $changeSet[\'extension\']->element=' . $changeSet['extension']->element); just before the if statement changed by this PR, you will see that it works.

@richard67 I performed clean beta3 installation and performed the same trick with column removal.

eid is 213 and element is really 'joomla' but not com_admin.

Schemas are checked via

SELECT `extensions`.`client_id`,`extensions`.`element`,`extensions`.`extension_id`,`extensions`.`folder`,`extensions`.`manifest_cache`,`extensions`.`name`,`extensions`.`type`,`schemas`.`version_id`
FROM `jos_schemas` AS `schemas`
INNER JOIN `jos_extensions` AS `extensions` ON `schemas`.`extension_id` = `extensions`.`extension_id`

#__schemas has a single record with extension_id = 213 which is files_joomla. Hence, #__schemas are unrelated to com_admin at all.

But the load changeset really has element=com_admin even though extension_id is 213 which is not com_admin:

object(stdClass)[723]
  public 'client_id' => int 0
  public 'element' => string 'com_admin' (length=9)
  public 'extension_id' => int 213
  public 'folder' => string '' (length=0)
  public 'manifest_cache' => string '{"name":"files_joomla","type":"file","creationDate":"July 2020","author":"Joomla! Project","copyright":"(C) 2005 - 2020 Open Source Matters. All rights reserved","authorEmail":"admin@joomla.org","authorUrl":"www.joomla.org","version":"4.0.0-beta3","description":"FILES_JOOMLA_XML_DESCRIPTION","group":""}' (length=304)
  public 'name' => string 'Joomla CMS' (length=10)
  public 'type' => string 'file' (length=4)
  public 'version_id' => string '4.0.0-2020-05-29' (length=16)
  public 'creationDate' => string 'July 2020' (length=9)
  public 'author' => string 'Joomla! Project' (length=15)
  public 'copyright' => string '(C) 2005 - 2020 Open Source Matters. All rights reserved' (length=56)
  public 'authorEmail' => string 'admin@joomla.org' (length=16)
  public 'authorUrl' => string 'www.joomla.org' (length=14)
  public 'version' => string '4.0.0-beta3' (length=11)
  public 'description' => string 'Joomla! 4 Content Management System.' (length=36)
  public 'group' => string '' (length=0)
  public 'author_info' => string 'admin@joomla.org<br>www.joomla.org' (length=34)
  public 'client' => string 'Site' (length=4)
  public 'client_translated' => string 'Site' (length=4)
  public 'type_translated' => string 'File' (length=4)
  public 'folder_translated' => string 'N/A' (length=3)

It's because of model code which auto-replaces element from joomla to com_admin to load the schema SQLs:

			if (strcmp($result->element, 'joomla') === 0)
			{
				$result->element = 'com_admin';

				if (!$this->getDefaultTextFilters())
				{
					$errorMessages[] = Text::_('COM_INSTALLER_MSG_DATABASE_FILTER_ERROR');
					$errorCount++;
				}
			}

So, checking for element=com_admin is correct.

And: the patch works.

But: the utf8mb4 conversion is still executed if #__utf8_conversion table is found and the conversion will be never finished due to new #__history table.

But: the utf8mb4 conversion is still executed if #__utf8_conversion table is found and the conversion will be never finished due to new #__history table.

For fixing this you need my other PR #30227 .

So please test both as described and then mark the test results on the issue tracker by using the "Test this" button, selecting the appropriate test result and then submitting.

Issue tracker item for this PR: https://issues.joomla.org/tracker/joomla-cms/30233

Issue tracker item for the other PR: https://issues.joomla.org/tracker/joomla-cms/30227

Thanks in advance.

I have tested this item ✅ successfully on ffd0ee2

I have tested this item ✅ successfully on ffd0ee2

RTC

Thanks guys for testing.