Python & MySQL - Performing Transactions

Transactions are a mechanism that ensures data consistency. Transactions have the following four properties −

• Atomicity − Either a transaction completes or nothing happens at all.

• Consistency − A transaction must start in a consistent state and leave the system in a consistent state.

• Isolation − Intermediate results of a transaction are not visible outside the current transaction.

• Durability − Once a transaction was committed, the effects are persistent, even after a system failure.

The Python DB API 2.0 provides two methods to either commit or rollback a transaction.

Example

You already know how to implement transactions. Here is again similar example −

# Prepare SQL query to DELETE required records
sql = "Delete from tutorials_tbl where tutorial_id = 2"
try:
   # Execute the SQL command
   cursor.execute(sql)
   # Commit your changes in the database
   db.commit()
except:
   # Rollback in case there is any error
   db.rollback()

COMMIT Operation

Commit is the operation, which gives a green signal to database to finalize the changes, and after this operation, no change can be reverted back.

Here is a simple example to call commit method.

db.commit()

ROLLBACK Operation

If you are not satisfied with one or more of the changes and you want to revert back those changes completely, then use rollback() method.

Here is a simple example to call rollback() method.

db.rollback()

Disconnecting Database

To disconnect Database connection, use close() method.

db.close()

If the connection to a database is closed by the user with the close() method, any outstanding transactions are rolled back by the DB. However, instead of depending on any of DB lower level implementation details, your application would be better off calling commit or rollback explicitly.