✨(backend) add fallback search & default ordering

Filter deleted documents from visited ones.
Set default ordering to the Find API search call (-updated_at)
BaseDocumentIndexer.search now returns a list of document ids instead of models.
Do not call the indexer in signals when SEARCH_INDEXER_CLASS is not defined
or properly configured.

Signed-off-by: Fabre Florian <ffabre@hybird.org>

src/backend/core/signals.py

@@ -2,10 +2,14 @@
 Declare and configure the signals for the impress core application
 """
 
+from functools import partial
+
+from django.db import transaction
 from django.db.models import signals
 from django.dispatch import receiver
 
 from . import models
+from .services.search_indexers import default_document_indexer
 from .tasks.find import trigger_document_indexer
 
 
@@ -16,7 +20,8 @@ def document_post_save(sender, instance, **kwargs):  # pylint: disable=unused-ar
     Note : Within the transaction we can have an empty content and a serialization
     error.
     """
-    trigger_document_indexer(instance, on_commit=True)
+    if default_document_indexer() is not None:
+        transaction.on_commit(partial(trigger_document_indexer, instance))
 
 
 @receiver(signals.post_save, sender=models.DocumentAccess)
@@ -24,5 +29,5 @@ def document_access_post_save(sender, instance, created, **kwargs):  # pylint: d
     """
     Asynchronous call to the document indexer at the end of the transaction.
     """
-    if not created:
-        trigger_document_indexer(instance.document, on_commit=True)
+    if not created and default_document_indexer() is not None:
+        transaction.on_commit(partial(trigger_document_indexer, instance.document))