Database Transactions and Error Handling

Module 8 covers the important topics of database transactions and error handling in SQLite

Module 8 covers the important topics of database transactions and error handling in SQLite. You will learn how to work with transactions to ensure data integrity and handle errors effectively in your Python code.

Understanding Database Transactions

A database transaction is a logical unit of work that consists of one or more database operations. Transactions ensure that a group of database operations are executed as a single, atomic unit. If any part of the transaction fails, all changes made within the transaction can be rolled back.

ACID Properties

Transactions in databases follow the ACID properties:

• Atomicity: Transactions are indivisible and treated as a single unit. Either all changes are applied, or none of them are.
• Consistency: Transactions bring the database from one consistent state to another. All data modifications within a transaction must adhere to defined rules and constraints.
• Isolation: Transactions occur independently of each other. The changes made within a transaction are isolated from other concurrent transactions until the changes are committed.
• Durability: Once a transaction is committed, its changes are permanent and survive any subsequent system failures.

Working with Transactions in SQLite

SQLite provides support for transactions through the BEGIN, COMMIT, and ROLLBACK statements.

Beginning a Transaction

To start a transaction, we use the BEGIN statement.

# Begin a transaction
connection.execute("BEGIN")

By default, SQLite starts a transaction automatically for each individual SQL statement. However, explicitly beginning a transaction allows us to group multiple SQL statements into a single transaction.

Committing a Transaction

To commit the changes made within a transaction, we use the COMMIT statement.

# Commit a transaction
connection.execute("COMMIT")

By committing a transaction, we make the changes permanent and ensure their durability.

Rolling Back a Transaction

If an error occurs or we want to discard the changes made within a transaction, we can roll back the transaction using the ROLLBACK statement.

# Roll back a transaction
connection.execute("ROLLBACK")

Rolling back a transaction undoes any changes made within the transaction, restoring the database to its state before the transaction began.

Error Handling in SQLite

When working with databases, it’s crucial to handle potential errors gracefully. SQLite provides error handling mechanisms through Python’s exception handling.

Catching SQLite Errors

To catch and handle SQLite errors, we can use the try and except statements in Python.

try:
    # Database operations
    connection.execute("...")
    # ...
except sqlite3.Error as e:
    # Handle the exception
    print(f"An error occurred: {e}")

By incorporating exception handling, we can provide informative error messages and take appropriate actions in case of any issues.

Auto-commit Mode and Transactions

By default, SQLite operates in auto-commit mode, where each SQL statement is treated as a separate transaction. However, explicitly using transactions can provide additional control and ensure the integrity of related operations.

Atomic Commit and Durability

In SQLite, changes made within a transaction are guaranteed to be atomic. When a transaction is committed, the changes are durable and survive any subsequent system failures.

By understanding database transactions and error handling in SQLite, you will have the knowledge to manage data changes effectively, maintain data integrity, and handle errors in your Python code.

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