Python
Session
Learn session management with sessionmaker.
Session
sessionmaker is a factory class that produces sessions. Bound to an Engine, each Session() call returns a new session. All database operations go through a session.
from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind=engine)
session = Session()
session.add(obj)
session.commit()
The session manages transactions; commit makes changes permanent, rollback undoes them. You close the session when done.
commit and rollback
Objects added to the session are not written to the database until commit() is called. On error, rollback() undoes the transaction.
session.add(User(name="Ayşe"))
session.commit() # make permanent
# or on error:
session.rollback() # undo
When done, close the session with session.close(). This returns the connection to the pool. You can open and close many sessions on the same engine.
Exercise Create Session and print its type
Start with from sqlalchemy import create_engine and from sqlalchemy.orm import sessionmaker. Define engine = create_engine("sqlite:///:memory:"). Create a session factory with Session = sessionmaker(bind=engine). Open a session with session = Session(). Print the class name with print(type(session).__name__).
Show example solution
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
engine = create_engine("sqlite:///:memory:")
Session = sessionmaker(bind=engine)
session = Session()
print(type(session).__name__)
Test yourself
-
Complete the sessionmaker call
from sqlalchemy.orm import sessionmaker
Session = ____(bind=engine)
Show answer
from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind=engine)
-
What does session.commit do?
- Closes the session
- Runs a query
- Makes changes permanent
- Creates an Engine
Show answer
Makes changes permanent — commit writes the session's changes to the database permanently.
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Match the Session concepts
- sessionmaker
- Is a session factory
- bind=engine
- Binds the engine
- session.add
- Adds an object
- session.commit
- Makes permanent
Next lesson: Defining models
