function db_insert($dbname, $data, $returnInsertId = FALSE)
{
$keys = array();
$values = array();
foreach ($data as $key => $value) {
$keys[] = $key;
$values[] = ":" . $key;
}
$keys = join(",", $keys);
$values = join(",", $values);
$insertquery = "INSERT INTO `{$dbname}` ({$keys}) VALUES ({$values})";
db_queryWith($insertquery, $data);
if ($returnInsertId) {
return $_ENV["DBPdo"]->lastInsertId();
}
}
function performTransaction($tid)
{
// TODO: Implement logic.
// 1. Get data from database via queryWith(..., array("tid" => $tid))
// 2. Load accounts from participants
// 3. Fail gracefully, if that didn't work (i.e. we don't have exactly one unverified transaction, excactly one account for each participants, etc.)
// 4. Perform account balance change
// 5. Mark as transaction as verified
// 6. Store updated data
//
// One potential problem: ensure database atomicity.
try {
$transaction = db_queryWith("SELECT * FROM transactions WHERE tid = :tid", array("tid" => $tid));
if ($transaction->rowCount() !== 1) {
return "Transaction does not exist.";
}
$transaction = $transaction->fetch();
$srcAccount = $transaction["sourceAccount"];
$targAccount = $transaction["targetAccount"];
$srcArray = db_queryWith("SELECT * FROM accounts WHERE userid =:userid", array("userid" => $srcAccount));
if ($srcArray->rowCount() !== 1) {
return "User does not exist";
}
$srcArray = $srcArray->fetch();
$targArray = db_queryWith("SELECT * FROM accounts WHERE userid= :userid", array("userid" => $targAccount));
if ($targArray->rowCount() !== 1) {
return "User does not exist";
}
$targArray = $targArray->fetch();
$srcBalance = $srcArray["balance"] - $transaction["volume"];
$targBalance = $targArray["balance"] + $transaction["volume"];
if ($srcBalance >= 0 && $targBalance >= 0) {
$firstTxn = db_queryWith("update accounts set balance =:srcBalance where userid=:userid", array("srcBalance" => $srcBalance, "userid" => $srcAccount));
if ($firstTxn) {
$secondTxn = db_queryWith("update accounts set balance=:targBalance where userid=:userid", array("targBalance" => $targBalance, "userid" => $targAccount));
if ($secondTxn) {
$verify = db_queryWith("update transactions set isVerified=1 where tid=:tid", array("tid" => $tid));
if ($verify) {
return "Transaction is Successful";
}
} else {
//Reverting Back the changes in DB since secondTxn failed
db_queryWith("update accounts set balance =:balance where userid=:userid", array("balance" => $srcArray->balance, "userid" => $srcAccount));
return "Transaction failed";
}
} else {
return "Transaction Failed";
}
} else {
return "Transaction failed due to insufficient balance";
}
} catch (Exception $exe) {
return "Transaction failed to perform";
}
}
