Declare a global object for multiple functions - php

Question

So I have a list of functions that i'm using in a web app. Most of the functions however, make calls to a database class. Here are two functions for example:
function add_post($userid,$body,$cat_id,$user_link){ //This function inserts new posts into the db
$db = new MysqliDb('localhost', 'root', 'root', 'my_db');
$now = date("Y-m-d H:i:s");
$insertData = array(
'user_id' => $userid,
'body' => $body,
'stamp' => $now,
'cat_id' => $cat_id,
'link' => $user_link
);
$db->insert('posts', $insertData);
}
function grab_username($userid){ //This function takes a user id, and returns the associated user_name
$db = new MysqliDb('localhost', 'root', 'root', 'my_db');
$params = array($userid);
$results = $db->rawQuery("SELECT username FROM users WHERE id = ?", $params);
//print_r($results);
foreach($results as $arrays){
foreach($arrays as $name){
return $name;
}
}
}
the problem is that I am constantly writing the line:
$db = new MysqliDb('localhost', 'root', 'root', 'my_db');
Is there a way I can declare the variable globally, have something more like this:
$db = new MysqliDb('localhost', 'root', 'root', 'my_db');
function add_post($userid,$body,$cat_id,$user_link){ //This function inserts new posts into the db
$now = date("Y-m-d H:i:s");
$insertData = array(
'user_id' => $userid,
'body' => $body,
'stamp' => $now,
'cat_id' => $cat_id,
'link' => $user_link
);
global $db->insert('posts', $insertData);
}

Answer 1

There are multiple ways to handle this but the best implementation can vary depending on the structure and needs of your action application.
You mentioned a global variable which would work, but is typically considered poor structure:
someFunction(){
global $db;
$db->insert('posts', $insertData);
}
Another method, which is slightly cleaner but still not as well organized is to pass the $db connection to the functions:
function myFunction( $db, ... ){
$db->query( // etc );
}
myFunction( $db );
A better version of this would be to organize your related functions in a class, and then inject the database:
class Posts {
public function listPosts( $db, ... ){
$db->query( // etc );
}
public function getPost( $db, ... ){
$db->query( // etc );
}
}
$posts = new Posts();
$posts->listPosts();
However, you can also decide to make these static methods, you could pass $db to the class constructor and store it, there are many choices.
You could also make a central wrapper class of your own that returns the connection. There are a million implementations but it's hard to specifically recommend one without knowing more about your application structure, how your classes share resources, how the application bootstraps everything - if it does. Etc

Answer 2

Try This:
db.php
class DB
{
public $conn;
private static $instance;
private function __construct()
{
$server = 'localhost';
$user = 'root';
$pass = 'root';
$database = 'my_db';
$this->conn = mysqli_connect($server,$user,$pass,$database);
}
public function query($sql)
{
$result = mysqli_query($this->conn,$sql);
return $result;
}
public static function getInstance()
{
if (!isset(self::$instance))
{
$object = __CLASS__;
self::$instance = new $object;
}
return self::$instance;
}
}
Now in any page you can do:
require("db.php");
$dbh = DB::getInstance();
$sql = "your sql query ..";
$dbh->query($sql);