Transaction management in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a transaction in PHP PDO.

PHP

<?php
$pdo->[1]();
?>

Drag options to blanks, or click blank then click option'

Acommit

BbeginTransaction

Crollback

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using commit() instead of beginTransaction() to start a transaction.

Using rollback() to start a transaction.

The beginTransaction() method starts a new transaction.

2fill in blank

medium

Complete the code to commit a transaction in PHP PDO.

PHP

<?php
$pdo->[1]();
?>

Drag options to blanks, or click blank then click option'

Acommit

BbeginTransaction

Crollback

Dprepare

Attempts:

3 left

💡 Hint

Common Mistakes

Using rollback() instead of commit() to save changes.

Using beginTransaction() instead of commit() here.

The commit() method saves all changes made during the transaction.

3fill in blank

hard

Fix the error in the code to rollback a transaction in PHP PDO.

PHP

<?php
$pdo->[1]();
?>

Drag options to blanks, or click blank then click option'

Arollback

Bcommit

CbeginTransaction

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using commit() instead of rollback() to cancel changes.

Using beginTransaction() instead of rollback() here.

The rollback() method cancels all changes made during the transaction.

4fill in blank

hard

Fill both blanks to correctly handle a transaction with error catching.

PHP

<?php
try {
    $pdo->[1]();
    // some database operations
    $pdo->[2]();
} catch (Exception $e) {
    $pdo->rollback();
}
?>

Drag options to blanks, or click blank then click option'

AbeginTransaction

Bcommit

Crollback

Dprepare

Attempts:

3 left

💡 Hint

Common Mistakes

Using rollback() to save changes.

Not starting the transaction before committing.

Start the transaction with beginTransaction() and save changes with commit(). If an error occurs, rollback cancels changes.

5fill in blank

hard

Fill all three blanks to handle a transaction with error catching and rollback.

PHP

<?php
try {
    $pdo->[1]();
    $stmt = $pdo->[2]("INSERT INTO users (name) VALUES ('John')");
    $stmt->execute();
    $pdo->[3]();
} catch (Exception $e) {
    $pdo->rollback();
}
?>

Drag options to blanks, or click blank then click option'

AbeginTransaction

Bprepare

Ccommit

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using execute() instead of prepare() for the statement.

Committing before executing the statement.

Not starting the transaction before preparing.

Start the transaction with beginTransaction(), prepare the SQL statement with prepare(), and commit changes with commit(). If an error occurs, rollback cancels changes.

Practice

1. What is the main purpose of using beginTransaction() in PHP when working with databases?

easy

A. To start a group of database operations that can be committed or rolled back together

B. To immediately save changes to the database

C. To close the database connection

D. To check if the database is available

Solution

1. Step 1: Understand the role of beginTransaction()

   This function starts a transaction, grouping multiple database changes into one unit.

2. Step 2: Recognize transaction benefits

   It allows committing all changes at once or rolling back if something goes wrong, ensuring data integrity.

3. Final Answer:

   To start a group of database operations that can be committed or rolled back together -> Option A

4. Quick Check:

   beginTransaction() starts a transaction [OK]

Hint: beginTransaction() starts safe grouped DB changes [OK]

Common Mistakes:

• Thinking it saves changes immediately
• Confusing it with closing the connection
• Assuming it checks database availability

2. Which of the following is the correct syntax to commit a transaction in PHP PDO?

easy

A. $pdo->commitTransaction();

B. $pdo->transactionCommit();

C. commit($pdo);

D. $pdo->commit();

Solution

1. Step 1: Recall PDO commit method

   The correct method to save all changes in a transaction is commit() called on the PDO object.

2. Step 2: Check method names

   Only $pdo->commit(); matches the correct PDO syntax; others are invalid method names.

3. Final Answer:

   $pdo->commit(); -> Option D

4. Quick Check:

   commit() saves transaction changes [OK]

Hint: Use $pdo->commit() to save transaction changes [OK]

Common Mistakes:

• Using incorrect method names like commitTransaction()
• Trying to call commit as a function with argument
• Confusing commit with rollback

3. What will be the output of the following PHP code snippet?

$pdo->beginTransaction();
$pdo->exec("INSERT INTO users (name) VALUES ('Alice')");
$pdo->rollBack();
echo $pdo->query("SELECT COUNT(*) FROM users")->fetchColumn();

medium

A. 0

B. 1

C. SyntaxError

D. Throws Exception

Solution

1. Step 1: Analyze transaction commands

   The code starts a transaction, inserts a user, then rolls back, undoing the insert.

2. Step 2: Check final data count

   Since the insert was rolled back, the users table remains unchanged, so count is 0.

3. Final Answer:

   0 -> Option A

4. Quick Check:

   rollBack() undoes insert, count = 0 [OK]

Hint: rollBack() cancels changes, so count stays zero [OK]

Common Mistakes:

• Assuming insert stays after rollBack()
• Confusing commit() with rollBack()
• Expecting syntax or runtime error

4. Identify the error in this PHP transaction code:

try {
  $pdo->beginTransaction();
  $pdo->exec("UPDATE accounts SET balance = balance - 100 WHERE id = 1");
  $pdo->exec("UPDATE accounts SET balance = balance + 100 WHERE id = 2");
  $pdo->commit();
} catch (Exception $e) {
  $pdo->commit();
}

medium

A. Missing beginTransaction() call

B. Using commit() in catch block instead of rollBack()

C. No exception handling block

D. Using exec() instead of query()

Solution

1. Step 1: Review transaction error handling

   In case of error, changes should be undone with rollBack(), not committed.

2. Step 2: Identify catch block mistake

   The catch block incorrectly calls commit(), which saves partial or faulty changes.

3. Final Answer:

   Using commit() in catch block instead of rollBack() -> Option B

4. Quick Check:

   Errors need rollBack(), not commit() [OK]

Hint: Use rollBack() on error, not commit() [OK]

Common Mistakes:

• Calling commit() in catch block
• Forgetting to handle exceptions
• Confusing exec() and query() methods

5. You want to transfer money between two accounts safely using PHP transactions. Which of the following sequences of steps is correct?

hard

A. Begin transaction, update sender balance, commit transaction, update receiver balance

B. Update sender balance, update receiver balance, begin transaction, commit transaction

C. Begin transaction, update sender balance, update receiver balance, commit transaction

D. Update sender balance, begin transaction, update receiver balance, commit transaction

Solution

1. Step 1: Understand transaction grouping

   All related updates must be inside the transaction to ensure atomicity.

2. Step 2: Check step order

   Starting with beginTransaction(), then updating both accounts, and finally committing ensures either all changes apply or none.

3. Final Answer:

   Begin transaction, update sender balance, update receiver balance, commit transaction -> Option C

4. Quick Check:

   All DB changes inside transaction before commit [OK]

Hint: Start transaction before updates, commit after all done [OK]

Common Mistakes:

• Updating before starting transaction
• Committing too early before all updates
• Not grouping all changes inside transaction