pdo connection position in php class - php

Question

I'm using PDO now and I have a number of classes.
Every time I use a class, I don't always use its database-related functions. Sometimes I keep using a class until at the end I might do some work with the database, like save this object to DB.
So I'm currently doing something like this:
class Something
{
protected $pdo;
function connect()
{
$this->pdo = new PDO( "mysql:host=".zConfig::read('hostname').";dbname=".zConfig::read('database'), zConfig::read('username'), zConfig::read('password'));
$this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
/* lots of functions doing lots of non-DB things */
function saveToDB()
{ $this->connect();
$this->pdo->prepare("Some SQL that saves some stuff");
// now do some DB-related pdo work
}
}
My question is - is this reasonable? Is this the way a lot of you code?
As I see it, there are 3 options:
The way I'm doing it - connecting to the database only in those
functions that are database related. But these means each time I run a DB-related function.
Open a connection in the constructor, in this case I only open it once, but also end up opening it even when I don't need it, so I feel like sometimes I'll be creating
connections for nothing.
On the other hand, I could use a singleton database class like this:
PDO Connections - max connections
I do have up to three related objects on a page, and sometimes I do and sometimes I don't need to connect to the DB more than once on a page. which design is safer?

Answer 1

You should use DI, in your class to instantiate a connection, when your object is defined ex:
class foo{
public $conn;
function __construct($conn){
$this->conn = $conn;
}
function doSomething(){
}
}
Now, if you find yourself, not wanting to instanciate a connection, whenever you
are on a page/work that does not need database connection, and significantly slows your page, while trying to connect, use the PDO attribute
ATT_PERSISTENT property like:
$conn = new PDO('mysql:host=localhost;dbname=xxx', 'xxx', 'xxx',
array( PDO::ATTR_PERSISTENT => true )
);
$object = new foo($conn);
Simply, once, you open a page, and connection is establish the ATTR_PERSISTENT method will store that connection, pretty much like sessions work, and will keep feeding your page, and helping you from creating a new connection to your db, every time you refresh a page, or go on to another page. Try, it.. and you'll see how faster your pages will load.

Answer 2

You can just use lazy way.
protected $pdo;
function connect()
{
if ($this->pdo === null)
{
$this->pdo = new PDO( "mysql:host=".zConfig::read('hostname').";dbname=".zConfig::read('database'), zConfig::read('username'), zConfig::read('password'));
$this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
}
Check this question.