mysql connection

Main.php
..................................................................

<?php 


class Main 
{

    private $_host = 'localhost';
    private $_username = 'root';
    private $_password = 'admin';
    private $_database = 'test';
    
    protected $connection;



    public function __construct()
    {
        if (!isset($this->connection)) {
            
            $this->connection = new mysqli($this->_host, $this->_username, $this->_password, $this->_database);
            
            if (!$this->connection) {
                echo 'Cannot connect to database server';
                exit;
            }            
        }    
        
        return $this->connection;     
    }
    
    public function getData($query)
    {        
        $result = $this->connection->query($query);
        
        if ($result == false) {
            return false;
        } 
        
        $rows = array();
        
        while ($row = $result->fetch_assoc()) {
            $rows[] = $row;
        }
        
        return $rows;
    }
        
    public function execute($query) 
    {
        $result = $this->connection->query($query);
        
        if ($result == false) {
            echo 'Error: cannot execute the command';
            return false;
        } else {
            return true;
        }        
    }
    
    public function delete($id, $table) 
    { 
        $query = "DELETE FROM $table WHERE id = $id";
        
        $result = $this->connection->query($query);
    
        if ($result == false) {
            echo 'Error: cannot delete id ' . $id . ' from table ' . $table;
            return false;
        } else {
            return true;
        }
    }
 
    public function escape_string($value)
    {
        return $this->connection->real_escape_string($value);
    }
}




?>


index.php
..................................................................
<?php 

include_once("Main.php");
$db = new Main();
$data = $db->getData('SELECT * FROM `test_table`');
print_r($data);
 ?>