Transaction processing in PDO

The benefits of using transactions ：

for instance ： Bank users A To the user B Transfer accounts 100 element , This operation is divided into two steps ：

(1)A Your account balance has been deducted 100.

(2)B The account balance of has increased 100.

If you don't use transactions , hypothesis (1) Execution succeeded , and (2) failed , The user B No receivables have been received , And users A The loss was in vain .

After using transactions , Regardless of (1) perhaps (2) Which step failed , All can be rolled back , That is, the account balance of both parties is restored to the previous state .

Not all databases provide transaction support , Such as mysql Medium Myisam The engine does not support transactions , But the new version defaults to innoDB The engine provides support for transactions .（RDBMS Most support transactions ,NoSQL Databases generally do not support transactions ）

Let's take a look at the specific code ：

<?php

$dsn      = "mysql:dbname=pdo;host=localhost";
$user     = "root";
$password = "root";
$dbh      = new PDO($dsn, $user, $password);
// Before using transactions , Turn off auto submit first . If you don't close it , When an exception occurs, it cannot be rolled back .
// According to the manual description ,ATTR_AUTOCOMMIT Property only in mysql,OCI(oracle),firebird Available in three databases 
$dbh->setAttribute(PDO::ATTR_AUTOCOMMIT, 0);
$cash = 100;

try {
    $dbh->beginTransaction();
    // user A Account deduction 100
    $sqlcmd        = "update transaction set useraccount=useraccount - {$cash} where username ='A'";
    $affected_rows = $dbh->exec($sqlcmd);
    if ($affected_rows > 0) {
        echo " user A Account deduction succeeded " . "<br>";
    } else {
        throw new Exception(" user A Account deduction failed ");
    }
    // user B Account increase 100
    $affected_rows = $dbh->exec("update transaction set useraccount=useraccount+{$cash} where username ='B'");
    
    if ($affected_rows > 0) {
        echo " user B Account increase succeeded " . "<br>";
    } else {
        throw new Exception(" user B Account addition failed ");
    }
    
    echo " Transfer succeeded ";
    // If the previous two steps are successful , Then commit the transaction 
    $dbh->commit();
}
catch (PDOException $e) // If an exception occurs in the previous two steps , Then roll back 
    {
    echo $e->getMessage();
    $dbh->rollback();
}
// After the use of things , Turn auto submit back on 
$dbh->setAttribute(PDO::ATTR_AUTOCOMMIT, 1);

?>