Avoid DetachedInstanceError in Flask-SQLAlchemy

gistfile1.py

# The following produces DetachedInstanceError

app = Flask(__name__)
db = SQLAlchemy(app)

class Foo(db.Model):
    id = db.Column(db.Integer, primary_key=True)
  
foo = Foo()
db.session.add(foo)
db.session.commit()
foo.id

>>> DetachedInstanceError: Instance <Foo at 0x10741ac10> is not bound to a Session; attribute refresh operation cannot proceed

# The following removes DetachedInstanceError

app = Flask(__name__)
db = SQLAlchemy(app, session_options{
    'expire_on_commit': False
})

class Foo(db.Model):
    id = db.Column(db.Integer, primary_key=True)
  
foo = Foo()
db.session.add(foo)
db.session.commit()
foo.id

>>> 1

But you don't close the session, the commit operation just expire the orm object, why does this lead to produces DetachedInstanceError ?
flask-sqlalchemy auto close when commit ?

Gosh this is a blast from the past @kalelsun 😄 I no longer work with Python or Flash / SQL Alchemy so I can't really answer your question, sorry, of course this very old code at this point so I have no idea if it is still relevant.