The "media_type" entity type does not exist.

Do you have a stack trace for this error? (Can be enabled at /admin/config/development/logging if Devel module is installed (or maybe even without).)
Does your index contain media entities?

Hi,
I got the same behaviour when trying to upgrade from search_api_solr 1.x to 3.x ( here from 1.3 to 3.8) while still using the contrib "Media Entity" Module 8.x-1.8.

Of course, Media are meant to be indexed.

any action on /admin/config/search/search-api/index/index_name/edit, /admin/config/search/search-api/index/index_name/fields ,
or drush sapi-c, sapi-r sapi-i will result in the following trace :

Drupal\Component\Plugin\Exception\PluginNotFoundException: The "media_type" entity type does not exist. in Drupal\Core\Entity\EntityTypeManager->getDefinition() (line 150 of core/lib/Drupal/Core/Entity/EntityTypeManager.php).

Drupal\Core\Entity\EntityTypeManager->getHandler('media_type', 'storage') (Line: 208)
Drupal\Core\Entity\EntityTypeManager->getStorage('media_type') (Line: 484)
Drupal\search_api_attachments\Plugin\search_api\processor\FilesExtractor->getFileFieldsAndFileEntityItems() (Line: 163)
Drupal\search_api_attachments\Plugin\search_api\processor\FilesExtractor->getPropertyDefinitions(NULL) (Line: 844)
Drupal\search_api\Entity\Index->getPropertyDefinitions(NULL) (Line: 434)
Drupal\search_api\Item\Field->getDataDefinition() (Line: 114)
Drupal\search_api\Plugin\search_api\processor\AddHierarchy->getHierarchyFields() (Line: 91)
Drupal\search_api\Plugin\search_api\processor\AddHierarchy::supportsIndex(Object)
call_user_func(Array, Object) (Line: 371)
Drupal\search_api\Form\IndexProcessorsForm->getAllProcessors() (Line: 103)
Drupal\search_api\Form\IndexProcessorsForm->form(Array, Object) (Line: 149)
Drupal\Core\Entity\EntityForm->buildForm(Array, Object)
call_user_func_array(Array, Array) (Line: 520)
Drupal\Core\Form\FormBuilder->retrieveForm('search_api_index_processors_form', Object) (Line: 277)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 91)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 573)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 151)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 68)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 694)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Is there any quick workaround to this ? Or should I definitly urge to switch to Media Entity in core ?

Brilliant, thanks a lot for the backtrace! Seems the flaw we need to fix in this module is insufficient error handling in the “Add hierarchy” processor. Please see, test and review the attached patch!

However, from the stack trace it’s apparent that there is also an underlying issue in the Search API Attachments module, so I posted a patch there was well: #3117949: Improve exception handling in FilesExtractor. Would be great if you could review that patch (independently of this one), too! Would be great to get both of these fixed.

PS: Hm, looking at this again, as the FilesExtractor::getPropertyDefinitions() method doesn’t follow its contract, by propagating/throwing exceptions it shouldn’t, the patch here wouldn’t actually do anything to resolve your problem. It should still be an improvement, but you’ll probably need the Attachments patch for the problem to go away.

Committed.
If possible, please still also give feedback on the Attachments patch in #3117949: Improve exception handling in FilesExtractor. (As said, the commit here will most likely not help with your problem.)