from mysql to PDO -- confused about the When and Where - php

Question

I'm trying to switch from building query strings and calling mysql_query() and embrace PDO. I've read a handful of tutorials, and understand the basic process of preparing a statement and assigning values to the placeholders.
What I don't understand is how to integrate this new technique into my existing web app.
Let me explain:
currently, I've got an init.php which is require_once'd on every page. It holds the database U/P and opens the database connection. With that loaded, I can sling queries left and right, willy AND nilly, anywhere I please without any further thought.
PDO strikes me as a much more deliberate approach. Do I still stuff all the U/P and connection handlers into my init file? Can I just work through my scripts and replace queries one-to-one with PDO statements?
Sorry for the simple question!

Answer 1

For what it is worth, I had the same issue and this is how I approached it. I divided the database functions into two different classes, Database and Query. I setup and open the database in my init function and then call instances of my Query class throughout the page, closing the queries each time I am done. Finally, I close the database.
The actual classes I use have some more error checking and other stuff I specifically, but here are the drafts I uses when putting the scheme together. Maybe it will be useful to you.
Database Class:
<?php
class Database {
private $db, $dbserver, $dbport, $dbname, $dbuser, $dbpassword;
//----------------------------------------------------------------------------------------------------------
//Function: __construct()
//----------------------------------------------------------------------------------------------------------
public function __construct($idbserver, $idbport, $idbname, $idbuser, $idbpassword)
{
$this->dbserver = $idbserver;
$this->dbport = $idbport;
$this->dbname = $idbname;
$this->dbuser = $idbuser;
$this->dbpassword = $idbpassword;
}
//----------------------------------------------------------------------------------------------------------
//Function: openDatabase()
//----------------------------------------------------------------------------------------------------------
public function openDatabase()
{
/* Create a new user db object with persistent database connection parameters */
try {
$this->db = new PDO("mysql:host=".$this->dbserver.";dbname=".$this->dbname.";port=".$this->dbport, $this->dbuser, $this->dbpassword, array(
PDO::ATTR_PERSISTENT => true
));
return true;
} catch (PDOException $e) {
print "Error!: " . $e->getMessage() . "<br/>";
die();
}
}
//----------------------------------------------------------------------------------------------------------
//Function: getDB
//----------------------------------------------------------------------------------------------------------
public function getDB()
{
//return the database
return $this->db;
}
//----------------------------------------------------------------------------------------------------------
//Function: getDBName
//----------------------------------------------------------------------------------------------------------
public function getDBName()
{
//return the database
return $this->dbname;
}
//----------------------------------------------------------------------------------------------------------
//Function: closeUserDatabase
//----------------------------------------------------------------------------------------------------------
public function closeDatabase()
{
//close the database
$this->db=null;
}
}
?>
Then my Query Class:
<?php
class Query {
private $db, $sql, $qresult;
//----------------------------------------------------------------------------------------------------------
//Function: __construct
//----------------------------------------------------------------------------------------------------------
public function __construct($idb, $isql)
{
$this->db = $idb;
$this->sql = $isql;
}
//----------------------------------------------------------------------------------------------------------
//Function: openQuery
//----------------------------------------------------------------------------------------------------------
public function openQuery($param)
{
/* assemble and run a query and return a result object */
//prepare the sql statement
//get the db object
$tempdb= $this->db->getDB();
$this->qresult = $tempdb->prepare($this->sql);
//bind parameters to the prepared statement
foreach ($param as $key => $value) {
$this->qresult->bindValue($key,$value);
}
return $this->qresult->execute();
}
//----------------------------------------------------------------------------------------------------------
//Function: fetchAssociative
//----------------------------------------------------------------------------------------------------------
public function fetchAssociative()
{
return $this->qresult->fetch(PDO::FETCH_ASSOC);
}
//----------------------------------------------------------------------------------------------------------
//Function: closeQuery
//----------------------------------------------------------------------------------------------------------
public function closeQuery()
{
$this->qresult = null;
}
}
?>
Then I set up the database in my init function:
//initialize the user database with buffered set true so we can use nested queries
$usrdb = new Database($udbserver, $udbport, $udbname, $udbuser, $udbpassword, array(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => true));
//open the database
$usrdb->openDatabase();
Then I call my query in the page:
//set up the sql
$sql = "SELECT * FROM Blah WHERE blahid = :filter";
//create the parameter array
$params = array(':filter'=>$filter);
//craetea new query
$q = new Query($usrdb, $sql);
//run the query
if ($q->openQuery($params)) {
//get the results if there are any
while ($row=$q->fetchAssociative()) {
$viewData['blahid']=$row['blahid'];
}
}
//clean up the query
$q->closeQuery();
After that I work with the results just like I always used to.

Answer 2

PDO works same way as old school approach. You still need to define connection and initialise object in order to query database.

Answer 3

I store the PDO database connection and retrieve an instance of it as a singleton.
Any place you need your database, to run a query or execute prepared statements, you use the singleton instance.
$db_handle = PDO_DBConnect::getInstance();
$stmt = $db_handle->prepare("SELECT * FROM users WHERE name= ?");
$result = $stmt->execute(array($cleaned_username));
...
If a class has multiple queries, you can store the handle in an instance variable,
$this->dbh = PDO_DBConnect::getInstance();
for convenience.
One other note is unlike pg_close or mysql_close, there is no close method for PDO. You simply set the db handle to null.