PHP Making database class static

Question

I just got started learning OOP in PHP, so forgive me if this is actually a very trivial question.

I have a class called Engine, and I have the class database, which extends engine. Some classes I call in scripts also extend engine. Now I want to make it so that I dont have to set the instance of $db to global in every method of other classes I have.

I thought the solution would be to make the MySqlDatabase class static, but somehow I get errors. Could someone tell me what I am doing wrong?

It's probably a very simple thing but im kind of stuck at the moment.

Thanks in advance!

<?php
class MySqlDatabase extends engine{

public static $connection;
public static $query;

function __construct(){
    MySqlDatabase::open_connection();
}

public static function open_connection(){
    self::$connection=mysqli_connect("localhost","XXX","XXX","XXX");
    mysqli_set_charset(self::$connection,'utf8') or die("Charset     error");

}

public static function close_connection(){
    mysqli_close(self::$connection);
}

 public static function con(){
     return self::$connection;
 }

 public static function query($query){
     $result = mysqli_query(self::$connection,$query);
     self::$query = $result;
     self::confirm_query($result);
     return $result;
 }

 public static function confirm_query($result){
     if(!$result){
         die("DB Query failed:".mysqli_error(self::$connection));
     }
 }

 public static function mysql_prep($string) {
     $escaped_string = mysqli_real_escape_string(self::$connection,$string);
     return $escaped_string;
 }

 public static function num_rows(){
     $result = mysqli_num_rows(self::$query);
     return $result;
 }

 public static function fetch_array(){
     $result = mysqli_fetch_array(self::$query);
     return $result;
 }

}

?>

Now when I want to get something from the DB I get errors when I use: '; ?>

Warning: mysqli_query() expects parameter 1 to be mysqli, null given in /home/devogdata/public_html/includes/dbconnect.php on line 39

Warning: mysqli_error() expects parameter 1 to be mysqli, null given in /home/devogdata/public_html/includes/dbconnect.php on line 47 DB Query failed:

when you call a static method, the __construct() function is not used — user1897253
– user1897253, Commented Mar 10, 2016 at 14:27

Vishnu Nair · Accepted Answer · 2016-03-10 14:32:27Z

3

Constructors are only called when an object is created, when you are calling a static method you call it from the class itself like this className::static_method() and not from the object. You will have to manually call the static method open_connection first and then the query so that it will instantiate the connection variable.

   MySqlDatabase::open_connection();
   MySqlDatabase::query('your sql query');

More information on static keyword and methods : http://php.net/manual/en/language.oop5.static.php

answered Mar 10, 2016 at 14:32

Vishnu Nair

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