Databases define transactions as logical units of work that can be
committed or rolled back as a single change, even if they operate
on multiple tables. All queries to a database are executed within
the context of a transaction, even if the database driver manages
them implicitly. This is called auto-commit
mode, in which the database driver creates a transaction for every
statement you execute, and commits that transaction after your
SQL statement has been executed. By default, all
Zend_Db Adapter classes operate in auto-commit mode.
Alternatively, you can specify the beginning and resolution of a
transaction, and thus control how many SQL queries are included in
a single group that is committed (or rolled back) as a single
operation. Use the beginTransaction() method to
initiate a transaction. Subsequent SQL statements are executed in
the context of the same transaction until you resolve it
explicitly.
To resolve the transaction, use either the commit() or
rollBack() methods. The commit()
method marks changes made during your transaction as committed, which
means the effects of these changes are shown in queries run in
other transactions.
The rollBack() method does the opposite: it discards
the changes made during your transaction. The changes are
effectively undone, and the state of the data returns to how it was
before you began your transaction. However, rolling back your
transaction has no effect on changes made by other transactions
running concurrently.
After you resolve this transaction, Zend_Db_Adapter
returns to auto-commit mode until you call
beginTransaction() again.
Example 210. Managing a Transaction to Ensure Consistency
<?php
// Start a transaction explicitly.
$db->beginTransaction();
try {
// Attempt to execute one or more queries:
$db->query(...);
$db->query(...);
$db->query(...);
// If all succeed, commit the transaction and all changes
// are committed at once.
$db->commit();
} catch (Exception $e) {
// If any of the queries failed and threw an exception,
// we want to roll back the whole transaction, reversing
// changes made in the transaction, even those that succeeded.
// Thus all changes are committed together, or none are.
$db->rollBack();
echo $e->getMessage();
}