How Can I Disable SQLAlchemy Caching to Prevent Data Inconsistencies?

Solving Caching Issues with SQLAlchemy

When using SQLAlchemy to insert and retrieve data from a database, caching issues can arise, leading to inconsistencies. This article investigates the common causes and provides a solution for disabling caching in SQLAlchemy.

Understanding SQLAlchemy Caching

SQLAlchemy maintains an identity map within each transaction, which acts as a cache for recently accessed objects. This optimizes performance by preventing multiple database queries for the same data. However, when data is updated externally to SQLAlchemy, this cache can cause problems by returning outdated results.

Disabling Caching

To resolve this issue, it is necessary to disable caching in SQLAlchemy. This can be achieved by setting the expire_on_commit flag to True on the mapper configuration. The following code demonstrates how to do this:

# Import the ORM classes
from sqlalchemy import Column, Integer, String, create_engine, sessionmaker

# Create an engine and session factory
engine = create_engine('mysql+pymysql://username:password@host/database')
Session = sessionmaker(bind=engine)

# Define the User class
class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)

    __mapper_args__ = {
        'expire_on_commit': True
    }

By setting expire_on_commit to True, SQLAlchemy will expire all objects in the identity map upon commit. This ensures that the latest data is always retrieved from the database.

Example

Consider the scenario described in the original question:

# Create a session
session = Session()

# Insert data into the database
new_user = User(name='John Doe')
session.add(new_user)
session.commit()

# Update the data directly in the database
connection = engine.connect()
cursor = connection.cursor()
cursor.execute("UPDATE users SET name='Jane Doe' WHERE>

With caching disabled, SQLAlchemy will return the updated user record (Jane Doe) instead of the outdated cached record (John Doe). This resolves the caching problem and ensures that the application always retrieves the latest data from the database.

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