Always read an entity's parent through get_parent when climbing up.

This should avoid the risk of `DetachedInstanceError` by retrieving the
object into the session if it's not available.

platypush/entities/_engine/repo/__init__.py

@@ -4,9 +4,8 @@ from typing import Dict, Iterable, Optional, Tuple
 from sqlalchemy.orm import Session
 
 from platypush.entities._base import Entity, EntityMapping
-
-# pylint: disable=no-name-in-module
 from platypush.entities._engine.repo.db import EntitiesDb
+from platypush.entities._engine.repo.helpers import get_parent
 from platypush.entities._engine.repo.merger import EntitiesMerger
 
 logger = logging.getLogger('entities')
@@ -98,7 +97,7 @@ class EntitiesRepository:
         """
         parent = entity
         while parent:
-            parent = self._merge.get_parent(session, entity)
+            parent = get_parent(session, entity)
             if parent:
                 entity = parent
 

platypush/entities/_engine/repo/db.py

@@ -7,6 +7,7 @@ from sqlalchemy.orm import Session
 
 from platypush.context import get_plugin
 from platypush.entities._base import Entity
+from .helpers import get_parent
 
 
 @dataclass
@@ -69,7 +70,7 @@ class EntitiesDb:
             batch.clear()
 
     def _split_entity_batches_for_flush(
-        self, entities: Iterable[Entity]
+        self, session: Session, entities: Iterable[Entity]
     ) -> List[List[Entity]]:
         """
         This method retrieves the root entities given a list of entities and
@@ -93,9 +94,10 @@ class EntitiesDb:
         for entity in entities:
             parent_key = None
             parent_id = entity.parent_id
-            if entity.parent:
-                parent_id = parent_id or entity.parent.id
-                parent_key = entity.parent.entity_key
+            parent = get_parent(session, entity)
+            if parent:
+                parent_id = parent_id or parent.id
+                parent_key = parent.entity_key
 
             if parent_id:
                 children_by_parent_id[parent_id][entity.entity_key] = entity
@@ -169,7 +171,7 @@ class EntitiesDb:
         Persist a set of entities.
         """
         # Get the "unwrapped" batches
-        batches = self._split_entity_batches_for_flush(entities)
+        batches = self._split_entity_batches_for_flush(session, entities)
 
         # Flush each batch as we process it
         for batch in batches:

platypush/entities/_engine/repo/helpers.py

@@ -0,0 +1,18 @@
+from typing import Optional
+
+from sqlalchemy.orm import Session, exc
+
+from platypush.entities import Entity
+
+
+def get_parent(session: Session, entity: Entity) -> Optional[Entity]:
+    """
+    Gets the parent of an entity, and it fetches if it's not available in
+    the current session.
+    """
+    try:
+        return entity.parent
+    except exc.DetachedInstanceError:
+        # Dirty fix for `Parent instance <...> is not bound to a Session;
+        # lazy load operation of attribute 'parent' cannot proceed`
+        return session.query(Entity).get(entity.parent_id) if entity.parent_id else None

platypush/entities/_engine/repo/merger.py

@@ -1,9 +1,11 @@
 from typing import Iterable, List, Optional
 
-from sqlalchemy.orm import Session, exc
+from sqlalchemy.orm import Session
 
 from platypush.entities._base import Entity, EntityMapping
 
+from .helpers import get_parent
+
 
 # pylint: disable=too-few-public-methods
 class EntitiesMerger:
@@ -93,7 +95,7 @@ class EntitiesMerger:
         appropriately rewired and that all the relevant objects are added to
         this session.
         """
-        parent = cls.get_parent(session, entity)
+        parent = get_parent(session, entity)
         if not parent:
             # No parent -> we can terminate the recursive climbing
             return entity
@@ -140,23 +142,6 @@ class EntitiesMerger:
         cls._sync_parent(session, existing_parent, new_entities, existing_entities)
         return entity
 
-    @staticmethod
-    def get_parent(session: Session, entity: Entity) -> Optional[Entity]:
-        """
-        Gets the parent of an entity, and it fetches if it's not available in
-        the current session.
-        """
-        try:
-            return entity.parent
-        except exc.DetachedInstanceError:
-            # Dirty fix for `Parent instance <...> is not bound to a Session;
-            # lazy load operation of attribute 'parent' cannot proceed`
-            return (
-                session.query(Entity).get(entity.parent_id)
-                if entity.parent_id
-                else None
-            )
-
     @staticmethod
     def _append_children(entity: Entity, *children: Entity):
         """