No active transaction - php

Question

I'm trying to use transactions with PDO, with the following code
try
{
$bdd = new PDO('mysql:host=HOSTNAME;dbname=DATABASENAME', 'USERNAME', 'PASSWORD');
}
catch(Exception $e)
{
die('Error : '.$e->getMessage());
}
$qry = 'UPDATE table SET field = CASE';
foreach($elements as $el){
$qry .= ' WHEN id = '. $el['id'] .' THEN '. $el['value'];
}
$qry .= ' ELSE field END, SET update_date = CASE';
foreach($elements as $el){
$qry .= ' WHEN id = '. $el['id'] .' THEN NOW()';
}
$qry .= ' ELSE update_date END';
$update = $bdd->prepare($qry);
$bdd->beginTransaction();
try {
$update->execute();
$bdd->commit();
}
catch(Exception $e) {
$bdd->rollback();
echo 'Error : '.$e->getMessage().'<br />';
echo 'N° : '.$e->getCode();
exit();
}
But I get the following error (and the table is not updated) :
Fatal error: Uncaught exception 'PDOException' with message 'There is no active transaction' in script.php:106
Stack trace:
#0 script.php(106): PDO->rollBack() #1 {main} thrown in script.php on line 106
(Line 106 is $bdd->rollback();)
I understand that it's telling me there is no transaction going on, but... there should be, with $bdd->rollback();...
Thanks for any help you can give !
EDIT : The database engine is MyISAM.
I have additional info after further testing :
I simplified the $qry in my question because I thought it was irrelevant, but it seems it isn't. The query I'm actually using is a much longer one, updating multiple elements with the following code (I also modified the code up there ^ in the original question) :
$qry = 'UPDATE table SET field = CASE';
foreach($elements as $el){
$qry .= ' WHEN id = '. $el['id'] .' THEN '. $el['value'];
}
$qry .= ' ELSE field END, SET update_date = CASE';
foreach($elements as $el){
$qry .= ' WHEN id = '. $el['id'] .' THEN NOW()';
}
$qry .= ' ELSE update_date END';
It seems that the length of the query and/or the number of updated lines is causing my issue :
when updating 72 lines at most (the query is 3463 characters long, all spaces included), the table is updated, and vardump($bdd->beginTransaction();) returns bool(true) (regardless of wether it's before or after the $update = $bdd->prepare($qry) line.
when updating 73 lines or more (the query is 3509 characters long, all spaces included, when it updates 73 lines), the table is not updated, and vardump($bdd->beginTransaction();) returns bool(false) (once again, regardless of wether it is before or after the $update = $bdd->prepare($qry) line.
Hints on why, and how I can fix it are appreciated.
Thanks again
EDIT 2 : I switched the engine to InnoDB. The issue still stands.

Answer 1

Move
$bdd->beginTransaction();
to above your query:
$qry = 'UPDATE table SET field = value'
$update = $bdd->prepare($qry);
EDIT:
You are using MyISAM engine which does not support transactions. Update your tables to use InnoDB.