it is correct for a transaction? - pdo

Question

I create a mysql transaction using pdo.
Please check my code is perfect or not. if its not correct then how i can set transaction correctly.
Do i need to use try block? how can i sort try block in this querys
if(is_null($this->pdo)){
return false;
} else {
$pdo = $this->pdo;
$pdo->beginTransaction();
$stmt = $pdo->prepare("SELECT mallu FROM users WHERE id=? LOCK IN SHARE MODE");
$stmt->execute([$alpharef]);
$reseller = $stmt->fetch();
$stmt = null;
$stmt = $pdo->prepare("UPDATE users SET mallu = mallu - :cost WHERE id=:userid");
$stmt->bindParam(':cost', $cost, PDO::PARAM_STR);
$stmt->bindParam(':userid', $alpharef, PDO::PARAM_INT);
if (stmt->execute() != true) {
$conn->rollBack();
return false
}
$stmt = null;
$dates = date("d-m-Y");
$statos = 0;
$stmt = $pdo->prepare("INSERT INTO request (rtyp, num, amount, cost, typ, usr, refid, tm, dates, status) VALUES (:rtyp, :num, :amount, :cost, :typ, :usr, :refid, NOW(), :dates, :status)");
$stmt->bindParam(':rtyp', $retyp, PDO::PARAM_STR);
............................................................
if (stmt->execute() != true) {
$conn->rollBack();
return false
}
$stmt = null;
$pdo->commit();
$this->msg = 'Request sent successfully';
return true;
}
$pdo = null;

Answer 1

Look at this pseudo-code. Try + catch helps you to handle failed transaction. All you have to do is to throw new exception when one of your sql's fail.
$pdo->beginTransaction();
try{
//DB_operation1
if (result==false){ throw new Exception("...message1...");}
//DB_operation2
if (result==false){ throw new Exception("...message2...");}
$pdo->commit();
}catch(exception $e){
$pdo->rollBack();
//do something with thrown message
}