PHP: using MySQL connections in singleton class - php

Question

I have a PHP web service that uses a singleton API class to call my web service methods. I have specific classes for each module in my application: Posts, Users, Login, etc. My API class is something like:
class API{
private static $api;
private $database;
private $post;
private $user;
public function __construct(){
$this->database = new DataBase();
$this->post = new Post();
$this->user = new User();
}
public static function getInstance(){
if(empty(self::$api)){
self::$api = new API();
}
return self::$api;
}
}
So, to get my user posts, I'd call $api->post->getPosts() inside the API class, or API::getPosts() outside the API class. The API class is a facade. Each child class has its own DataBase instance. For example, Post and User has the following:
class User{
private $database;
public function __construct(){
$this->database = new DataBase();
}
}
My DataBase constructor is something like:
public function __construct() {
try{
$this->db = new \PDO(
"mysql:host=$this->host;dbname=$this->base;",
$this->user, $this->pass,
array(\PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES 'utf8'")
);
}catch(\PDOException $e){
echo "<b>Error:</b> {$e->getMessage()} in <b>{$e->getFile()}</b> on line <b>{$e->getLine()}</b>";
die();
}
}
The problem is: each request uses up to five MySQL connections to generate the response. For example: a regular request includes login validation, get user info, get posts info, etc. I was wondering if I can pass the DataBase instance from the API facade to the children classes. I tried something like:
public static function getDatabase(){
$api = self::getInstance();
return $api->database;
}
But every time I call API::getDatabase() from the children classes, I get a MySQL TOO MANY CONNECTIONS error, because this method calls the API __construct() and creates a new DataBase instance.
Any idea how can I recycle my DataBase instance, or connections, to avoid connections wasting?
UPDATE
As suggested bellow, I used the dependency injection pattern to pass my DataBase object from the API facade to its children:
public function __construct(){
$this->database = new DataBase();
$this->post = new Post($this->database);
$this->user = new User($this->database);
}

Answer 1

(To take this out of "Unanswered".)
The commenters suggested and the OP verified:
Use the dependency injection pattern to pass the DataBase object from the API facade to its children:
private function __construct(){
$this->database = new DataBase();
$this->post = new Post($this->database);
$this->user = new User($this->database);
}
(Actually private was suggested but not confirmed.)