Using class database connection in other class - php

Question

I have a class with a connection to a database
$db = new db();
class db {
public $server = 'localhost';
public $user = '';
public $passwd = '******';
public $db = '';
public $dbCon;
function __construct() {
$this->dbCon = mysqli_connect($this->server, $this->user, $this->passwd, $this->db);
}
function __destruct() {
mysqli_close($this->dbCon);
}
}
Now i want to make an other class and using the connection like this:
class Categories (
function GetCategory($cat) {
$myQuery = "SELECT * FROM test GROUP BY $cat";
$results = mysqli_query($this->dbCon, $myQuery);
return $results;
}
)
How can i use the connection in a other class?
Can somebody help me out whit this?

Answer 1

Make the $dbCon in your db class a static variable, so you can access it from category's using db::$dbcon as the connection variable. You could also make a static function returning the static dbcon variable, usefull tot check if it is actually a link and not null.
This is just one solution of many possibilities, but probably the easiest to implement because it isn't likely you need more connections to a db, so a static is perfect for it.
A static is nothing more then a variable living in the namespace it is defined in, you don't need to initialize the class in order to access it. It's value is shared across all instances of the object, so creating multiple DB class instances allows you tot just return a static if it was set in a previous DB class instance.
class db{
static $link;
static function connect(){
if(self::$link = mysqli_connect(....)){
return self::$link;
} else {
die('could not connect to db');
}
}
static function getcon(){
return isset(self::$link) ? self::$link : self::connect();
}
}
class Categories{
function GetCategory($cat){
$myQuery = "SELECT * FROM test GROUP BY $cat";
return mysqli_query(db::getcon(), $myQuery);
}
}

Answer 2

Create an object of the db class in the categories class. Then use that object to query the db accordingly. Also make sure you use a static variable in the db class. SO that the connection variable is created once and will be used all along the application.
Your db class may look like this
class db {
public $server = 'localhost';
public $user = '';
public $passwd = '******';
public $db = '';
public static $dbCon;
function __construct() {
$this->dbCon = mysqli_connect($this->server, $this->user, $this->passwd, $this->db);
}
function __destruct() {
mysqli_close($this->dbCon);
}
}
Your categories class may look like this
class Categories {
$connection=db::$dbCon;
if(!$connection){
$db=new db();
$connection=db::$dbCon;
}
function GetCategory($cat) {
$myQuery = "SELECT * FROM test GROUP BY $cat";
$results = mysqli_query($this->connection, $myQuery);
return $results;
}
}