php pdo prepared statment and transitions - php

Question

I am trying to write a function that is supposed to receive any MySQL statement and apply it,
The basic idea is not to repeat needed code to write to Database, well what is needed to connect to Database is creating new PDO object, starting a transaction and preparing a statement, binding values to it, executing it,
so every time I want to access the Database I don't have to repeat these steps,
Here is a function that does that :
==============================================================================================
protected function applyQuery($statement, $bindparameters , &$values , $selectStatement, &$result){
try{
$dbh = DataBase::setConnection();// new PDO("MySQL= .....");
$dbh->beginTransaction();
$stmt = $dbh->prepare($statement);
if($bindparameters == true){
foreach($values as $key => $value){
$stmt->bindValue($key, $value);
}
}
$stmt->execute();
$dbh->commit();
if($selectStatement == TRUE){
$result = $stmt->fetchAll(PDO::FETCH_ASSOC);
}
}catch (PDOException $e){
$dbh->rollBack();
throw DataBase::$Errors[0];
}
}
============================================================================================
$statement = the desired statement (e.g 'SELECT * from users WHERE username = :username')///
$bindparameters = do we need to bind values (in this examples yes) so its value TRUE///
&$values = array by reference in this case equals = (':username' => 'User');///
$selectStatement = tells if using SELECT in statement ,in this case TRUE///
$result = array by reference in this case the final fetch result will be stored in it///
so in this example we get the following call to the function :
applyQuery('SELECT * from users WHERE username = :username', TRUE ,array(':username' => 'User') , TRUE , result )
My question is : will this code work ?
is the logical sequence of what it does and should do make sense ?
whats the difference between $stmt->execute and $dbh->commit ?
is omitting any line will cause failure to achieve the desired result
Please understand that I did lookup what is PDO and read a lot but unable to answer these questions!