SQLModel/SQLAlchemy updating parent is causing new children - sqlalchemy

Question

I am using SQLModel to maintain a Region, which contain multiple areas.
These areas have in turn events through a many to many link table.
Creating my region with areas work fine, but if I update information in the region it duplicates all areas, all referencing the main region.
I am looking for a simplish way to make sure that if the region is the same, areas are the same and events on the areas are the same, the existing objects (and their ID's) are used.
This is my model:
class Region(SQLModel, table=True):
region_id: int = Field(primary_key=True)
name: str
description: Optional[str]
sourceAbbreviation: str
chapter: str
areas: Optional[List["Area"]] = Relationship(back_populates="region")
class AreaEvent(SQLModel, table=True):
area_id: int = Field(foreign_key="area.area_id", primary_key=True)
event_id: int = Field(foreign_key="event.event_id", primary_key=True)
class Area(SQLModel, table=True):
area_id: int = Field(primary_key=True)
name: str
description: Optional[str]
region_id: int = Field(foreign_key="region.region_id")
region: Optional["Region"] = Relationship(back_populates="areas")
events: Optional[List['Event']] = Relationship(back_populates="areas", link_model=AreaEvent)
class Event(SQLModel, table=True):
event_id: int = Field(primary_key=True)
name: str
areas: Optional[List[Area]] = Relationship(back_populates="events", link_model=AreaEvent)
And this is my retrieval method - nb: the get_adventureparts method returns a region with child areas.
#router.post("/region/{region_name}", response_model=RegionResponse)
async def add_region(
region_name: str,
sourceAbbreviation: str,
chapter: str,
session: Session = Depends(get_session)
):
db_region = session.query(Region).options(selectinload(Region.areas)).filter(Region.name == region_name.lower(),
Region.sourceAbbreviation == sourceAbbreviation.lower()).one_or_none()
if db_region is not None:
new_region = get_adventureparts(db_region)
for key, value in vars(new_region).items():
if key != "_sa_instance_state" and value is not None:
setattr(db_region, key, value)
session.commit()
region = session.query(Region).get(db_region.region_id)
else:
new_region = get_adventureparts(
Region(name=region_name.lower(), description="", sourceAbbreviation=sourceAbbreviation.lower(),
chapter=chapter))
session.add(new_region)
session.commit()
region = session.query(Region).get(new_region.region_id)
return RegionResponse.from_orm(region)