如何检查PHP中是否存在活动的MySQLi连接？

Question

I have extended my Database Models from the mysqli class, but i don't want it to reconnect everytime i instantiate a new model, because it really slows down the whole script.

I have a Database class extends from mysqli, and other model classes extending from Database.

My Database class looks like this :

class Database extends mysqli {

    // some properties ...

    public function __construct() {
        parent::__construct(MySQL_HOST, MySQL_USER, MySQL_PASS, MySQL_DATABASE);
        $this->set_charset(MySQL_CHARACTER_SET);

        // initializing stuff ..             
    }

    // some other methods...     
}

A sample model class would look like this :

class User extends Database {
    protected $table = "users";

public function __construct($id = null) {
    // Calling the parent constructor.
    parent::__construct();
    if($id) {
        // This is the current logged-in user.
        // Importing all session data into this object.
        $this->data->import($this->session->all());
        // ^^ This imports all the user related session data into this object 
        // i don't think it's relevant but i'll leave it here just in case.
    }                
}

My question is,

• How can i check if there is an active mysqli connection?

• How can i prevent it from reconnecting and use the active connection instead?

• What other approaches can i follow?

• Should i migrate to PDO, do i have to? Why?

P.S.: Migrating to PDO will be a lot of rework, as i've already built things over mysqli.