# PDO::beginTransaction

(PHP 5 >= 5.1.0, PHP 7, PECL pdo >= 0.1.0)

PDO::beginTransaction Initiates a transaction

### Description

public bool PDO::beginTransaction ( void )

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.

### Return Values

Returns TRUE on success or FALSE on failure.

### Errors/Exceptions

Throws a PDOException if there is already a transaction started or the driver does not support transactions.

Note: An exception is raised even when the PDO::ATTR_ERRMODE attribute is not PDO::ERRMODE_EXCEPTION.

### Examples

Example #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 */
?>

### User Contributed Notes 15 notes

47
steve at fancyguy dot com
3 years ago
The nested transaction example here is great, but it's missing a key piece of the puzzle.  Commits will commit everything, I only wanted commits to actually commit when the outermost commit has been completed.  This can be done in InnoDB with savepoints.

<?php

class Database extends PDO
{

protected
$transactionCount = 0; public function beginTransaction() { if (!$this->transactionCounter++) {
return
parent::beginTransaction();
}

$this->exec('SAVEPOINT trans'.$this->transactionCounter);
return
$this->transactionCounter >= 0; } public function commit() { if (!--$this->transactionCounter) {
return
parent::commit();
}
return
$this->transactionCounter >= 0; } public function rollback() { if (--$this->transactionCounter) {

$this->exec('ROLLBACK TO trans'.$this->transactionCounter + 1);
return
true;
}
return
parent::rollback();
}

}
38
bitluni
5 years ago
You can generate problems with nested beginTransaction and commit calls.
example:

beginTransaction()
do imprortant stuff
call method
beginTransaction()
basic stuff 1
basic stuff 2
commit()
do most important stuff
commit()

Won't work and is dangerous since you could close your transaction too early with the nested commit().

There is no need to mess you code and pass like a bool which indicate if transaction is already running. You could just overload the beginTransaction() and commit() in your PDO wrapper like this:

<?php
class Database extends \\PDO
{
protected
$transactionCounter = 0; function beginTransaction() { if(!$this->transactionCounter++)
return
parent::beginTransaction();
return
$this->transactionCounter >= 0; } function commit() { if(!--$this->transactionCounter)
return
parent::commit();
return
$this->transactionCounter >= 0; } function rollback() { if($this->transactionCounter >= 0)
{

$this->transactionCounter = 0; return parent::rollback(); }$this->transactionCounter = 0;
return
false;
}
//...
}
?>
kesler dot alwin at gmail dot com
2 years ago

$this->exec('ROLLBACK TO trans'.$this->transactionCounter + 1);

with

$this->exec('ROLLBACK TO trans'.($this->transactionCounter + 1));
rjohnson at intepro dot us
9 years ago
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;
}
}
}

?>
drm at melp dot nl
10 years ago
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;
}

}
ludwig dot green at gmail dot com
7 years ago
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.
geompse at gmail dot com
8 years ago
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
eddi13
3 years ago
after TRUNCATE TABLE table  just as DELETE FROM table, so if whole table was deleted, aborts the transaction. And the rollback will not be passible.
dbeecher at tekops dot com
9 years ago
// 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: " . $e->getMessage(); }; cristian at crishk dot com 1 year ago OK I'm finding a solution for "NESTED" transactions in MySQL, and as you know in the MySQL documentation says that it's not possible to have transactions within transactions. I was trying to use the Database class propossed here in http://php.net/manual/en/pdo.begintransaction.php but unfortunately that's wrong for many things related to the control flow that I have been solved with the following code (LOOK THE EXAMPLE AT THE END, CarOwner) <?php class TransactionController extends \\PDO { public static$warn_rollback_was_thrown = false;
public static
$transaction_rollbacked = false; public function __construct() { parent :: __construct( ... connection info ... ); } public static$nest = 0;
public function
reset()
{

TransactionController :: $transaction_rollbacked = false; TransactionController ::$warn_rollback_was_thrown = false;

TransactionController :: $nest = 0; } function beginTransaction() {$result = null;
if (
TransactionController :: $nest == 0) {$this->reset();

$result =$this->beginTransaction();
}

TransactionController :: $nest++; return$result;
}

public function
commit()
{

$result = null; if ( TransactionController ::$nest == 0 &&
!
TransactionController :: $transaction_rollbacked && ! TransactionController ::$warn_rollback_was_thrown) {

$result = parent :: commit(); } TransactionController ::$nest--;
return
$result; } public function rollback() {$result = null;
if (
TransactionController :: $nest >= 0) { if ( TransactionController ::$nest == 0) {

$result = parent :: rollback(); TransactionController ::$transaction_rollbacked = true;
}
else {

TransactionController  :: $warn_rollback_was_thrown = true; } } TransactionController ::$nest--;
return
$result; } public function transactionFailed() { return TransactionController ::$warn_rollback_was_thrown === true;
}

// to force rollback you can only do it from $nest = 0 public function forceRollback() { if ( TransactionController ::$nest === 0) {

throws new \PDOException();
}
}
}

?>
Steel Brain
3 years ago
The example is misleading, Typically data definition language clauses (DDL) will trigger the database engine to automatically commit. It means that if you drop a table, that query will be executed regardless of the transaction.
Ref-Mysql:
http://dev.mysql.com/doc/refman/5.0/en/implicit-commit.html
-1
sasi dot viragelet at gmail dot com
1 year ago

try {

$pdo->beginTransaction(); // ... whatever db actions you have and then:$sql_insert = 'INSERT INTO a (a_id, a_name, a_date)
VALUES (:a_id, :a_name CURRENT_TIMESTAMP)';

$stmt =$pdo->prepare($sql_insert);$stmt->bindValue(':_id', $id);$stmt->bindValue(':a_name', $name);$stmt->execute();

$pdo->commit(); } catch (\PDOException$e) {

$pdo->rollBack(); http_response_code(500); header("Content-type: text/plain"); echo$e;
exit();

}

Notice the sytax error? There's a missing comma that just slips through every gate of surveillance:

"...UES (:a_id, :a_name CURR..." :: between the to be binded value and current timestamp command. The missing comma will not generate any error no syntax error, no database error. Though this record will never or partially make it. This will just silently fail. The story gets rough if you build your other dependencies on the transactions unmovable foot-stones of trust.

Just imagine you have some basic records in your transaction that you really wanna ensure ends up correctly in your db. And these records have a foreign constraint relation with another record. (That of course if you'd include in the transaction would throw you a big red error(–for who don't get it: transaction will first attempt to write everything into a temporary place, where it will get checked before everything gets into its permanent place, so constraints cannot be checked for something that don't exist yet.)) So you have a constraint that's based on the trust PDO will throw an error if something gets screwed, so what, you'll just place that insertion after the commit was successful. (Without any doublecheck.)

What happens you will get some partial records in your database without a relation that just might be important. You will that way be able to build up very sophisticated strange behaviours in your application. So pay attention!
arth dot inbox at mail dot ru
4 years ago
Strange behavior with pdo_firebird driver:

<?php
$dbh = new PDO ('','','',array( PDO :: ATTR_PERSISTENT=>true));$dbh->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION );
$dbh -> exec ( "select 1;" ); //should be autocommitted try { //$dbh->commit/rollback here fixes the issue;

$dbh -> beginTransaction (); // <- fails "with there is already an active transaction"$dbh -> exec ( "select 1;" );

$dbh -> commit (); } catch ( Exception$e )
{

$dbh -> rollBack (); } ?> Anonymous 10 years ago beginTransaction will through a PDOException if you execute it while a PDO transaction is already active. Additionally the PDO engine doesn't seem to provide any way of determining if there is a transaction "in flight" so if you might be calling a function from within another function that starts a transaction you'll have to wrap the beginTransaction () call in a try .. catch block. -12 mtjo62 at gmail dot com 4 years ago For the PDO driver for the Firebird server, you have to explicitly disable autocommit to initiate the transaction as well as explicitly enable autocommit to commit it.$dbh->setAttribute( PDO::ATTR_AUTOCOMMIT, 0 );
$dbh->beginTransaction(); /** Query block */$dbh->commit();
\$dbh->setAttribute( PDO::ATTR_AUTOCOMMIT, 1 );