How do I use multiple classes in PHP - php

Question

I'm very new to oop in php, so far i'm using multiple classes that I made in one php file, such as:
class Style {
//stuff
}
class User {
//other stuff
}
And many more, yet i'm having an issue on how to connect to mysql within these classes, if I use $db = new Mysqli(); how will I be able to make queries from inside classes? what if i'm trying to make my own connector class like so:
class Connection extends mysqli {
public function __construct($host, $user, $pass, $db) {
parent::__construct($host, $user, $pass, $db);
if (mysqli_connect_error()) {
die('Connect Error (' . mysqli_connect_errno() . ') '
. mysqli_connect_error());
}
}
}
How can I be able to make queries from within different classes? Or what's a better way of using oop in php correctly? with multiple classes to organize different parts of code?
Any help or tips will be appreciated, thanks. What about using PDO? does that make everything easier?

Answer 1

class Style {
public function __construct($conn) {
$this->conn = $conn;
//use $this->conn in the class
}
}
$db = new Mysqli();
$style = new Style($db);
I think the first example is the preferred method, however you could create a simple registry class and use that to store a $db object etc.
If possible I would probably use PDO but that doesn't solve this issue.

Answer 2

Since you are extending the mysqli class you will have access to the functions as you would if you instantiated that class by itself (so long as those functions aren't private). Some folks though (including myself) will instantiate the DB connection in their own custom class with a database connection, then inject that class into classes that need it.
class MyDatabase {
private $this->dbi;
public function __construct() {}
public function connectDB($host, $user, $pass, $db)) {
//You can do this in the constructor too, doesn't have to be its own function
$this->dbi = new mysqli($host, $user, $pass, $db);
}
public function getDBI() {
return $this->dbi;
}
}
You can add all the functions you want to your own class (or an extended class), you can also have any class that needs a database extend your DB class. But that isn't really preferred (each class will have a different db class/connection). The easiest is probably to import your DB connection into your class. Either through the constructor or another function;
class MyClass {
private $this->database;
public function __construct($db) {
$this->database = $db->getDBI();
}
public function query($q) {
//Of course, clean your data first, and best practices use prepared statements
$result = $this->database->query($q);
return $result;
}
}
Then make your database connection and inject it into your class.
$db = new MyDatabase();
$db->connectDB('localhost', 'username', 'password', 'mydb');
$class = new MyClass($db);
$resultSet = $class->query("SELECT * FROM MyTable"); //Obviously anything the user could add here is to not be trusted.

Answer 3

using PDO will give you a lot of functions and flexebilty and it has many drivers built-in.
to make what you are trying to do here is a sample :
STEP 1 :
Make a Main class that will handle your database :
class app extends PDO {
protected $database_hostname = "localhost";
protected $database_username = "root";
protected $database_password = "";
protected $database_name = "testdb";
protected $database_type = "mysqli";
public function __construct() {
try {
parent::__construct($this->database_type . ':host=' . $this->database_hostname . ';dbname=' . $this->database_name, $this->database_username, $this->database_password, array(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION));
} catch (PDOException $e) {
echo 'ERROR: ' . $e->getMessage();
}
}
}
STEP 2 :
then you need to initilze a globale variable as your Database :
$db= new app() ;
STEP 3 :
include a local variable to handle database in the other classes :
class User{
public $db ;
}
STEP 4 :
in the constructor of the other classes ( user for exemple ) you need to pass the local variable by reference to the globale variable :
class User{
public $db ;
public function __construct(){
global $db;
$this->db =& $db;
}
}
STEP 5 :
then if you want to execute a request from inside a class you do it by the local variable :
$this->db->query("SELECT * FROM user");
and from the outside just by using : $db->query("SELECT * FROM user");
I hope that helped !