How to update custom fields of the Sessions model in Flask?

Question

Flask

Good afternoon!
I'm trying to learn Flask. Out of the box, the documentation is intelligible and understandable, but I needed to store in the database in the sessions table, in addition to the regular data for flask_sessions, several of my own fields.
Here is the model I created:

class Sessions(db.Model):
  __table_args__ = { 'extend_existing': True }

  user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable = True)
  room_id = db.Column(db.Integer, db.ForeignKey('room.id'), nullable = True)

Now I need to update the user_id.
In theory, I need to know the id of the record in the database.
I can't figure out how to get to it.
I tried to get to id like this:
print(app.session_interface.sql_session_model.id)
but the output is:
Sessions.id
In general, I expected it to look something like:

session.user_id = 1
session.commit()

But apparently not everything is so simple (
Actually, the question is:
How to correctly change the user_id field for the current session in the database?
UPD:
I found a solution, but it seems to me that there should be something more correct than this:

row = db.session.query(Sessions).filter_by(session_id = 'session:%s'%session.sid).first()
row.user_id = 1
db.session.commit()