PDO::rollback after using prepared statement - pdo

Question

I understand that in order to prevent injection attack, PDO::prepare first sends the query to the server then the parameters go later; Now, I feel this introduces another problem: that implies there cannot be rollback after PDO::execute, or am I missing something?
I have two tables 1 and 2 in an application. The two tables are not supposed to contain the same row. When I use INSERT INTO table1 SELECT FROM Table2, I want to DELETE FROM table2 if the INSERT query succeeds. And if either of the queries fails, I want to rollback. So I have the following code:
$dbConn->beginTransaction();
$stmt1 = $dbConn->prepare( "INSERT INTO table1 ( field1, field2, field3 )
SELECT field1, field2, field3 FROM table2 WHERE field4 = :field4" );
$stmt1->execute( array( $field4 ) );
$stmt2 = $dbConn->prepare( "DELETE FROM table2 WHERE field4 = :field4" );
$stmt2->execute( array( $field4 ) );
if ( $stmt1->rowCount() > 0 && $stmt2->rowCount() > 0 )
{
$dbConn->commit();
return true;
}
else
{
$dbConn->rollBack();
return false;
}
Without prepared statement, this is very easy; but with it, it looks like difficult; has anyone done something like this before?
Thanks.

Answer 1

This isn't difficult and from what I can tell should work fine. However I would restructure the code to use exceptions:
try {
$dbConn->beginTransaction();
$stmt1 = $dbConn->prepare( "INSERT INTO table1 ( field1, field2, field3 )
SELECT field1, field2, field3 FROM table2 WHERE field4 = :field4" );
$stmt1->execute( array( $field4 ) );
$stmt2 = $dbConn->prepare( "DELETE FROM table2 WHERE field4 = :field4" );
$stmt2->execute( array( $field4 ) );
if ( $stmt1->rowCount() > 0 && $stmt2->rowCount() > 0 )
{
$dbConn->commit();
return true;
}
else
{
throw new LogicException('Unequal row counts.');
}
} catch (Exception $e) {
$dbConn->rollBack();
if ($e instanceof LogicException) {
// just return
return false;
} else {
// otherwise rethrow because something we didnt expect to go
// wrong did
throw $e;
}
}
This way we also roll back if something else generates an exception like PDO or some other thing we may be doing as part of our data preparation.