search_api_attachments_entity_view() crashes with the SearchAPI Database backend

Problem/Motivation

I set up SAA with an attachment field on a node, and my SAPI index with the Database backend.

When a node is viewed, either as a search result or on its own, it crashes with:

Drupal\search_api\SearchApiException: Unknown field in filter clause: 'nid'. in Drupal\search_api_db\Plugin\search_api\backend\Database->createDbCondition() (line 2513 of /var/www/html/repos/search_api/modules/search_api_db/src/Plugin/search_api/backend/Database.php).

Drupal\search_api_db\Plugin\search_api\backend\Database->createDbQuery() (Line: 1837)
Drupal\search_api_db\Plugin\search_api\backend\Database->search() (Line: 483)
Drupal\search_api\Entity\Server->search() (Line: 549)
Drupal\search_api\Query\Query->execute() (Line: 138)
search_api_attachments_entity_view()

The DB backend's tables don't have a field for the node ID, or even any entity type ID.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes