Don't use the entities cache when upserting entities.

This may make things a bit less optimal, but it's probably the only
possible solution that preserves my sanity.

Managing upserts of cached instances that were previously made transient
and expunged from the session is far from easy, and the management of
recursive parent/children relationships only add one more layer of
complexity (and that management is already complex enough in its current
implementation).

platypush/entities/_engine/repo/__init__.py

@@ -37,29 +37,28 @@ class EntitiesRepository:
         logger.info('Entities cache initialized')
 
     def get(
-        self, session: Session, entities: Iterable[Entity]
+        self, session: Session, entities: Iterable[Entity], use_cache=True
     ) -> Dict[Tuple[str, str], Entity]:
         """
         Given a set of entity objects, it returns those that already exist
         (or have the same ``entity_key``). It looks up both the cache and the
         database.
         """
-        entities_map: Dict[Tuple[str, str], Entity] = {
-            e.entity_key: e for e in entities
-        }
-
-        # Fetch the entities that exist in the cache
         existing_entities = {}
-        # TODO UNCOMMENT THIS CODE TO ACTUALLY USE THE CACHE!
+        if not use_cache:
-        # existing_entities = {
+            existing_entities = self._db.fetch(session, entities)
-        #     key: self._entities_cache.by_external_id_and_plugin[key]
+            self._cache.update(*existing_entities.values())
-        #     for key in entities_map.keys()
+        else:
-        #     if key in self._entities_cache.by_external_id_and_plugin
+            # Fetch the entities that exist in the cache
-        # }
+            existing_entities = {
+                e.entity_key: self._cache.get(e) for e in entities if self._cache.get(e)
+            }
 
             # Retrieve from the database the entities that miss from the cache
             cache_miss_entities = {
-            key: e for key, e in entities_map.items() if key not in existing_entities
+                e.entity_key: e
+                for e in entities
+                if e.entity_key not in existing_entities
             }
 
             cache_miss_existing_entities = self._db.fetch(
@@ -71,6 +70,7 @@ class EntitiesRepository:
 
             # Return the union of the cached + retrieved entities
             existing_entities.update(cache_miss_existing_entities)
+
         return existing_entities
 
     def save(self, *entities: Entity) -> Iterable[Entity]:

platypush/entities/_engine/repo/merger.py

@@ -49,7 +49,7 @@ class EntitiesMerger:
         (Recursive) inner implementation of the entity merge logic.
         """
         processed_entities = []
-        existing_entities.update(self._repo.get(session, entities))
+        existing_entities.update(self._repo.get(session, entities, use_cache=False))
 
         # Retrieve existing records and merge them
         for entity in entities:
@@ -96,7 +96,7 @@ class EntitiesMerger:
         # If there's no parent_id but there is a parent object, try to fetch
         # its stored version
         if not parent_id and parent:
-            batch = list(self._repo.get(session, [parent]).values())
+            batch = list(self._repo.get(session, [parent], use_cache=False).values())
 
             # If the parent is already stored, use its ID
             if batch: