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Commit and Roll Back

This lesson adds a second row to the tutorial table and then undoes it with a rollback, so you can see what a transaction keeps and what it discards. It follows Save a Row and Read It Back.

Before you start

You need what the earlier lessons set up:

  • first_saved_row.py from Save a Row and Read It Back printed Rows seen by a new connection: [(1, 'my first saved row')], so the table pycubrid_quickstart_notes exists with one row;
  • the same folder and an active virtual environment (in a new terminal, run source .venv/bin/activate again).

Write the program

Create first_rollback.py in the same folder, with the same SETTINGS:

import pycubrid

SETTINGS = {"host": "localhost", "port": 33000, "database": "testdb", "user": "dba", "password": ""}

conn = pycubrid.connect(**SETTINGS)
cur = conn.cursor()

# 1. Insert a second row, but do not commit it.
cur.execute(
    "INSERT INTO pycubrid_quickstart_notes (id, note) VALUES (?, ?)",
    (2, "this row is rolled back"),
)
cur.execute("SELECT id, note FROM pycubrid_quickstart_notes ORDER BY id")
print("Before rollback:", cur.fetchall())

# 2. Undo it.
conn.rollback()  # rollback discards everything since the last commit

cur.execute("SELECT id, note FROM pycubrid_quickstart_notes ORDER BY id")
print("After rollback:", cur.fetchall())
cur.close()
conn.close()

Run it

python first_rollback.py

The second row is visible inside the transaction, then gone after the rollback:

Before rollback: [(1, 'my first saved row'), (2, 'this row is rolled back')]
After rollback: [(1, 'my first saved row')]

What the program did

  • A transaction groups your changes until you end it. pycubrid starts one for you: autocommit is off by default, so nothing is permanent until you call commit().
  • Inside the transaction, your own connection already sees the uncommitted row, which is why the first SELECT shows two rows.
  • rollback() ends the transaction and discards every change since the last commit(). The row saved in the previous lesson stays, because it was committed.
  • Closing a connection without commit() does not save its changes either. Commit what you want to keep before you close.

You can run first_rollback.py again: each run adds and removes the same second row, so it prints the same two lines. If the program is interrupted before the rollback, the server discards the uncommitted row when the connection ends.

Next step

You have saved and undone changes. Last, finish safely: remove the tutorial table and, if you used it, the Docker lab.