scoped_session(sessionmaker()) or plain sessionmaker() in sqlalchemy?

I am using SQlAlchemy in my web project. What should I use - scoped_session(sessionmaker()) or plain sessionmaker() - and why? Or should I use something else?

## model.py
from sqlalchemy import *
from sqlalchemy.orm import *

engine = create_engine('mysql://dbUser:dbPassword@dbServer:dbPort/dbName',
pool_recycle=3600, echo=False)
metadata = MetaData(engine)
Session = scoped_session(sessionmaker())
Session.configure(bind=engine)
user = Table('user', metadata, autoload=True)

class User(object):
pass

usermapper = mapper(User, user)

## some other python file called abc.py
from models import *

def getalluser():
   session = Session()  
   session.query(User).all()
   session.flush()
   session.close()

## onemore file defg.py
from models import *

def updateuser():
   session = Session()  
   session.query(User).filter(User.user_id == '4').update({User.user_lname: 'villkoo'})
   session.commit()
   session.flush()
   session.close()

I create a session = Session() object for each request and I close it. Am I doing the right thing or is there a better way to do it?

Solution 1:

Reading the documentation is recommended:

the scoped_session() function is provided which produces a thread-managed registry of Session objects. It is commonly used in web applications so that a single global variable can be used to safely represent transactional sessions with sets of objects, localized to a single thread.

In short, use scoped_session() for thread safety.

Solution 2:

Scoped_session at every method will give you a thread of local session which you cannot obtain beforehand (like at the module level).It's not needed to open a new session in every method, You can use a global session , Create a session only when the global session is not available. i.e you can write a method which returns a session and add it to the init.py inside your package.

Solution 3:

FYI, when using flask-sqlalchemy, the session object provided is by default a scoped session object.

http://flask-sqlalchemy.pocoo.org/2.3/quickstart/#road-to-enlightenment