Modelling of parent/children relationships on entity level

platypush/entities/_base.py

@@ -8,6 +8,7 @@ import pkgutil
 from sqlalchemy import (
     Boolean,
     Column,
+    ForeignKey,
     Index,
     Integer,
     String,
@@ -16,7 +17,7 @@ from sqlalchemy import (
     UniqueConstraint,
     inspect as schema_inspect,
 )
-from sqlalchemy.orm import ColumnProperty
+from sqlalchemy.orm import ColumnProperty, Mapped, backref, relationship
 
 from platypush.common.db import Base
 from platypush.message import JSONAble
@@ -38,6 +39,12 @@ class Entity(Base):
     description = Column(String)
     type = Column(String, nullable=False, index=True)
     plugin = Column(String, nullable=False)
+    parent_id = Column(
+        Integer,
+        ForeignKey(f'{__tablename__}.id', ondelete='CASCADE'),
+        nullable=True,
+    )
+
     data = Column(JSON, default=dict)
     meta = Column(JSON, default=dict)
     is_read_only = Column(Boolean, default=False)
@@ -50,6 +57,19 @@ class Entity(Base):
         DateTime(timezone=False), default=datetime.utcnow(), onupdate=datetime.utcnow()
     )
 
+    parent: Mapped['Entity'] = relationship(
+        'Entity',
+        remote_side=[id],
+        uselist=False,
+        lazy=True,
+        backref=backref(
+            'children',
+            remote_side=[parent_id],
+            uselist=True,
+            cascade='all, delete-orphan',
+        ),
+    )
+
     UniqueConstraint(external_id, plugin)
 
     __table_args__ = (

platypush/entities/_engine.py

@@ -6,6 +6,7 @@ from time import time
 from typing import Iterable, List, Optional
 
 from sqlalchemy import and_, or_
+from sqlalchemy.exc import InvalidRequestError
 from sqlalchemy.orm import Session, make_transient
 
 from platypush.context import get_bus, get_plugin
@@ -258,7 +259,10 @@ class EntitiesEngine(Thread):
             session.commit()
 
             for e in entities:
+                try:
                     session.expunge(e)
+                except InvalidRequestError:
+                    pass
 
         with self._entities_cache_lock:
             for entity in entities: