'select_book' is not a supported key
>>> [!note] Migrated issue
<!-- Drupal.org comment -->
<!-- Migrated from issue #3590928. -->
Reported by: [fgm](https://www.drupal.org/user/27985)
Related to !182
>>>
<h3 id="summary-problem-motivation">Problem/Motivation</h3>
<p>After upgrade a site to the latest 11.3.9 and Book to 3.0.4, <code>drush updb</code> emitted warnings:</p>
<pre><pre>> [notice] Update started: book_update_103008<br>> [warning] Schema errors for book.settings with the following errors: book.settings:allowed_types.0 variable type is string but applied schema class is Drupal\Core\Config\Schema\Mapping, book.settings:allowed_types.1 variable type is string but applied schema class is Drupal\Core\Config\Schema\Mapping, book.settings:child_type missing schema. These errors mean there is configuration that does not comply with its schema. This is not a fatal error, but it is recommended to fix these issues. For more information on configuration schemas, check out <a href="https://www.drupal.org/docs/drupal-apis/configuration-api/configuration-schemametadata">the documentation</a>.<br>> [notice] Update completed: book_update_103008<br>> [notice] Update started: book_update_103009<br>> [warning] Schema errors for book.settings with the following errors: book.settings:allowed_types.0 variable type is string but applied schema class is Drupal\Core\Config\Schema\Mapping, book.settings:allowed_types.1 variable type is string but applied schema class is Drupal\Core\Config\Schema\Mapping, book.settings:child_type missing schema. These errors mean there is configuration that does not comply with its schema. This is not a fatal error, but it is recommended to fix these issues. For more information on configuration schemas, check out <a href="https://www.drupal.org/docs/drupal-apis/configuration-api/configuration-schemametadata">the documentation</a>.<br>....<br>> [notice] Update started: book_post_update_prepopulate_max_depth_and_selected_book_settings<br>> [warning] Schema errors for block.block.osinett_booknavigation with the following errors: block.block.osinett_booknavigation:settings.select_book missing schema. These errors mean there is configuration that does not comply with its schema. This is not a fatal error, but it is recommended to fix these issues. For more information on configuration schemas, check out <a href="https://www.drupal.org/docs/drupal-apis/configuration-api/configuration-schemametadata">the documentation</a>.<br>> [warning] Schema errors for block.block.stark_book with the following errors: block.block.stark_book:settings.select_book missing schema. These errors mean there is configuration that does not comply with its schema. This is not a fatal error, but it is recommended to fix these issues. For more information on configuration schemas, check out <a href="https://www.drupal.org/docs/drupal-apis/configuration-api/configuration-schemametadata">the documentation</a>.<br>> [notice] Update completed: book_post_update_prepopulate_max_depth_and_selected_book_settings<br>...<br>> [warning] Message: Schema errors for book.settings with the following errors:<br>> book.settings:allowed_types.0 variable type is string but applied schema<br>> class is Drupal\Core\Config\Schema\Mapping, book.settings:allowed_types.1<br>> variable type is string but applied schema class is<br>> Drupal\Core\Config\Schema\Mapping, book.settings:child_type missing schema.<br>> These errors mean there is configuration that does not comply with its<br>> schema. This is not a fatal error, but it is recommended to fix these issues.<br>> For more information on configuration schemas, check out the documentation<br>> [1].<br>><br>> [1] https://www.drupal.org/docs/drupal-apis/configuration-api/configuration-schemametadata</pre></pre><p>Once the upgrade complete once gets errors like this in the site status report:</p>
<p><img src="https://www.drupal.org/files/issues/2026-05-19/Screenshot%202026-05-19%20at%2018.46.10.png" alt="config schema error for book on blocks"></p>
<h4 id="summary-steps-reproduce">Steps to reproduce</h4>
<ul>
<li>Start with a site on Drupal 11.0.x and Book 1.0x.</li>
<li>Upgrade to Drupal 11.1, 11.2, 11.3</li>
<li>Once on 11.3, upgrade Book to 3.0.4</li>
<li>run <code>drush updb</code>
</li></ul>
<h3 id="summary-proposed-resolution">Proposed resolution</h3>
<h3 id="summary-remaining-tasks">Remaining tasks</h3>
<h3 id="summary-ui-changes">User interface changes</h3>
<h3 id="summary-api-changes">API changes</h3>
<h3 id="summary-data-model-changes">Data model changes</h3>
issue