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(PHP 5 >= 5.1.0, PECL pdo >= 0.1.0)
PDO::beginTransaction — Initiates a transaction
Turns off autocommit mode. While autocommit mode is turned off, changes made to the database via the PDO object instance are not committed until you end the transaction by calling PDO::commit(). Calling PDO::rollBack() will roll back all changes to the database and return the connection to autocommit mode.
Some databases, including MySQL, automatically issue an implicit COMMIT when a database definition language (DDL) statement such as DROP TABLE or CREATE TABLE is issued within a transaction. The implicit COMMIT will prevent you from rolling back any other changes within the transaction boundary.
Gibt bei Erfolg TRUE zurück. Im Fehlerfall wird FALSE zurückgegeben.
Beispiel #1 Roll back a transaction
The following example begins a transaction and issues two statements that modify the database before rolling back the changes. On MySQL, however, the DROP TABLE statement automatically commits the transaction so that none of the changes in the transaction are rolled back.
<?php
/* Begin a transaction, turning off autocommit */
$dbh->beginTransaction();
/* Change the database schema and data */
$sth = $dbh->exec("DROP TABLE fruit");
$sth = $dbh->exec("UPDATE dessert
SET name = 'hamburger'");
/* Recognize mistake and roll back changes */
$dbh->rollBack();
/* Database connection is now back in autocommit mode */
?>
be aware that you also can not use TRUNCATE TABLE as this statement will trigger a commit just like CREATE TABLE or DROP TABLE
it is best to only use SELECT, UPDATE and DELETE within a transaction, all other statements may cause commits thus breaking the atomicity of your transactions and their ability to rollback
obviously you can use DELETE FROM <table> instead of TRUNCATE TABLE but be aware that there are differences between both statements, for example TRUNCATE resets the auto_increment value while DELETE does not.
With Oracle, any structure statement will do an implicit commit.
So : ALTER TABLE "my_table" DROP COLUMN "my_column";
Can't be rolled back !
Hope this will save time for others
If you are using PDO::SQLITE and need to support a high level of concurrency with locking, try preparing your statements prior to calling beginTransaction() and you may also need to call closeCursor() on SELECT statements to prevent the driver from thinking that there are open transactions.
Here's an example (Windows, PHP version 5.2.8). We test this by opening 2 browser tabs to this script and running them at the same time. If we put the beginTransaction before the prepare, the second browser tab would hit the catch block and the commit would throw another PDOException indicating that transactions were still open.
<?php
$conn = new PDO('sqlite:C:\path\to\file.sqlite');
$stmt = $conn->prepare('INSERT INTO my_table(my_id, my_value) VALUES(?, ?)');
$waiting = true; // Set a loop condition to test for
while($waiting) {
try {
$conn->beginTransaction();
for($i=0; $i < 10; $i++) {
$stmt->bindValue(1, $i, PDO::PARAM_INT);
$stmt->bindValue(2, 'TEST', PDO::PARAM_STR);
$stmt->execute();
sleep(1);
}
$conn->commit();
$waiting = false;
} catch(PDOException $e) {
if(stripos($e->getMessage(), 'DATABASE IS LOCKED') !== false) {
// This should be specific to SQLite, sleep for 0.25 seconds
// and try again. We do have to commit the open transaction first though
$conn->commit();
usleep(250000);
} else {
$conn->rollBack();
throw $e;
}
}
}
?>
// If you need to set an ISOLATION level or LOCK MODE it needs to be done BEFORE you make the BeginTransaction() call...
//
// **note** you should always check result codes on operations and do error handling. This sample code
// assumes all the calls work so that the order of operations is accurate and easy to see
//
// THIS IS using the PECL PDO::INFORMIX module, running on fedora core 6, php 5.2.4
//
// This is the correct way to address an informix -243 error (could not position within table) when there
// is no ISAM error indicating a table corruption. A -243 can happen (if the table/indexes, etc., are ok)
// if a row is locked. The code below sets the LOCK MODE to wait 2 minutes (120 seconds) before
// giving up. In this example you get READ COMMITTED rows, if you don't need read committed
// but just need to get whatever data is there (ignoring locked rows, etc.) instead of
// "SET LOCK MODE TO WAIT 120" you could "SET ISOLATION TO DIRTY READ".
//
// In informix you *must* manage how you do reads because it is very easy to trigger a
// lock table overflow (which downs the instance) if you have lots of rows, are using joins
// and have many updates happening.
//
// e.g.,
$sql= "SELECT FIRST 50 * FROM mytable WHERE mystuff=1 ORDER BY myid"; /* define SQL query */
try /* create an exception handler */
{
$dbh = new PDO("informix:host=......");
if ($dbh) /* did we connect? */
{
$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$dbh->query("SET LOCK MODE TO WAIT 120")
# ----------------
# open transaction cursor
# ----------------
if ( $dbh->beginTransaction() ) # explicitly open cursor
{
try /* open exception handler */
{
$stmt = $dbh->prepare($sql, array(PDO::ATTR_CURSOR => PDO::CURSOR_SCROLL));
$stmt->execute();
while ($row = $stmt->fetch(PDO::FETCH_NUM, PDO::FETCH_ORI_NEXT))
{
$data = $row[0] . "\t" . $row[1] . "\t" . $row[2] . "\t" . $row[3] . "\t" . $row[4] . "\t" . $row[5] . "\t" . $row[6] . "\t" . $row[7] . "\n" . $row[8] ;
//print $data;
print_r($row);
};
$stmt = null;
}
catch (PDOException $e)
{
print "Query Failed!\n\n";
print "DBA FAIL:" . $e->getMessage();
};
$dbh->rollback(); # abort any changes (ie. $dbh->commit()
$dbh = null; # close connection
}
else
{
# we should never get here, it should go to the exception handler
print "Unable to establish connection...\n\n";
};
};
}
catch (Exception $e)
{
$dbh->rollback();
echo "Failed: " . $e->getMessage();
};
Here is a way of testing that your transaction has started when using MySQL's InnoDB tables. It will fail if you are using MySQL's MyISAM tables, which do not support transactions but will also not return an error when using them.
<?
// Begin the transaction
$dbh->beginTransaction();
// To verify that a transaction has started, try to create an (illegal for InnoDB) nested transaction.
// If it works, the first transaction did not start correctly or is unsupported (such as on MyISAM tables)
try {
$dbh->beginTransaction();
die('Cancelling, Transaction was not properly started');
} catch (PDOException $e) {
print "Transaction is running (because trying another one failed)\n";
}
?>
In response to "Anonymous / 20-Dec-2007 03:04"
You could also extend the PDO class and hold a private flag to check if a transaction is already started.
class MyPDO extends PDO {
protected $hasActiveTransaction = false;
function beginTransaction () {
if ( $this->hasActiveTransaction ) {
return false;
} else {
$this->hasActiveTransaction = parent::beginTransaction ();
return $this->hasActiveTransaction;
}
}
function commit () {
parent::commit ();
$this->hasActiveTransaction = false;
}
function rollback () {
parent::rollback ();
$this->hasActiveTransaction = false;
}
}
beginTransaction will through a PDOException if you execute it while a PDO transaction is already active. Additionally the PDO engine doesn't seem to provide any way of determining if there is a transaction "in flight" so if you might be calling a function from within another function that starts a transaction you'll have to wrap the beginTransaction () call in a try .. catch block.
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