Question

So I started this tutorial as an intro to the PHP PDO. Up until now I’ve only worked with basic mysql_* type queries.

I’ve noticed that, throughout the tutorial, the connect -> do action -> disconnect pattern is repeated, and only the do action part ever changes.

In a real-world setting, would it be a good idea to eliminate repetition by creating a function into which queries can be passed?

For example:

a function for handling queries:

<?php
function databaseDo($action) {
    $db_hostname = 'localhost';
    $db_username = 'root';
    $db_password = 'root';

    try {
        // Establish DB connection
        $dbh = new PDO("mysql:host=$hostname;dbname=mysql", 
                $db_username, $db_password);
        echo 'Connected to database';

        // Do something
        $action($dbh);        // <- here goes whatever action we wish to perform

        // Close connection
        $dbh = null;
    } 
    catch(PDOException $e) {
        echo $e->getMessage();
    }
?>

Then, suppose I want to perform the action in the first example of the PDO tutorial, I would set it like this:

<?php
// Define action
$insert = function($dbh) {
    $query = "INSERT INTO animals(animal_type, animal_name)
                VALUES ('kiwi', 'troy')";
    $exec = $dbh->exec($query);
    echo $exec; 
};

// Perform action
databaseDo($insert);
?>

Scope of $dbh

I am using $dbh as an argument. Is this the proper way of passing a variable to a function like this without making it global?

Answer 1

Yes it is a great idea
A suggestion would be making a database helper class that uses the singleton pattern.. Something like

abstract class DB
   {

    protected static $instance;

    protected $db;

    protected static $host = 'host';
    protected static $user = 'user';
    protected static $pass = 'pass';
    protected static $database;

    public static function getInstance()
    {
        if (!isset(self::$instance)) self::$instance = new static();

        return self::$instance;
    }

    public static function doStatement($statement, array $parameters)
    {

         $handler = self::sql()->prepare($statement);
         $handler->closeCursor();
         $handler->execute($parameters);
         return $handler;
    }
    protected function __construct()
    {
        $this->db = new PDO(sprintf('mysql:host=%s;dbname=%s', static::$host, static::$database), static::$user, static::$pass);
        $this->db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        $this->db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_OBJ);

    }

    public static function db()
    {
        return static::getInstance()->db;
    }
}

class Main extends DB
{
    protected static $database = 'db';
}

to use it

$db = Main::getInstance();
$results = $db::doStatement('SELECT * FROM table WHERE id = :id', array(':id' => 5));

Now this is just very basic, and much more would need to be added (Exception handling, more/better helper methods, etc) but I have used something like this in many projects.