SQLAlchemy is a popular Object-Relational Mapping (ORM) library in Python that provides a convenient way to interact with databases. One important aspect of SQLAlchemy is the session management, which allows you to manage and track changes to your database objects.

By default, SQLAlchemy sessions are not synchronized with the database, meaning that changes made to objects in a session are not immediately persisted in the database. Instead, SQLAlchemy collects these changes and applies them in batch when necessary, optimizing the usage of database connections.

However, in some cases, you may need to ensure that the session is immediately synchronized with the database, for example, when you need to read back values that were just committed in the same session. SQLAlchemy provides a way to configure a session to behave synchronously.

Enable Session Synchronization

To enable session synchronization in SQLAlchemy, you can use the synchronize_session parameter while committing changes to the session. It can be set to the following values:

• False (default): SQLAlchemy will not synchronize the session with the database. This is the most efficient option, but changes made in the current session will not be immediately reflected in subsequent queries within the same session.
• True: SQLAlchemy will immediately synchronize the session with the database after the commit operation. This ensures that subsequent queries within the same session will see the most up-to-date changes made in the session.
• 'evaluate': SQLAlchemy will evaluate changes made in the current session and synchronize only the affected objects with the database. This can be useful if you want to limit the synchronization to specific objects.

Here is an example of using the synchronize_session parameter:

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

# Create engine and session
engine = create_engine('postgresql://username:password@localhost/mydatabase')
Session = sessionmaker(bind=engine)
session = Session()

# Make changes to objects in the session
# ...

# Commit changes with session synchronization enabled
session.commit(synchronize_session=True)

By setting synchronize_session to True, the session will be immediately synchronized with the database after the commit operation. Subsequent queries within the same session will see the latest changes made in the session.

Conclusion

The synchronize_session parameter in SQLAlchemy allows you to control when and how the session is synchronized with the database. Choosing the appropriate synchronization strategy depends on your specific use-case and requirements. By understanding this feature, you can optimize your SQLAlchemy sessions for efficient data manipulation and retrieval.

Remember to choose the synchronization strategy that best suits your needs to ensure the desired behavior and performance of your application.