How can I use variable from class in another class

Question

I wants to call methods in a class, using db connection from another class.

initializing.php

// load the configs, AFTER this I SHOULD HAVE CONSTANTS
require_once('myconfigs.php');

// load some function , some HELPER
require_once(LIB_PATH.DS.'functions.php');

// load the core objects
require_once(LIB_PATH.DS.'database.php');
$database = MySQLDatabaseConnection::connection();

the database.php

require_once('myconfigs.php');

require_once(LIB_PATH.DS.'initializing.php');

class MySQLDatabaseConnection {

    private static $instance;

    private function __construct(){

    }

    private function __clone(){

    }

    public static function connection(){

        if ( !isset( self::$instance ) ) {
            self::$instance = new MySQLi(DBSERVER, DBUSER, DBPASSWORD, DBNAME);
            if ( self::$instance->connect_error ) {
                throw new Exception('MySQL connection failed: '. self::$instance->connect_error);
            }
        }

        return self::$instance;

    }



}

the listproducts.php

It is for some testing, after this in DbPlus class I want to create CRUD methods, but looks like simple echo doesnt works :/

require_once('initializing.php');

class DbPlus extends MySQLDatabaseConnection{

    public $database = parent::connection();

    public function read(){
        $query = "SELECT name, price_in, price_out, category_products_id FROM products";
        $data = $database->query($query);

        while ( $row = $data->fetch_object()) {
            echo $row->name;
        }
    }

}

$dbplus = new DbPLus;
$dbplus->read();

Im getting this error

Parse error: syntax error, unexpected '(', expecting ',' or ';' in D:\XAMPP\htdocs\xxx\includes\listproducts.php on line 19

I dont have clue where does unexpected '(' comes from.

Any idea? Thank you

Please do not use global state to share DB connection between several instance. Instead use something like this: http://stackoverflow.com/a/11369679/727208 — tereško, Apr 04 '14 at 15:07

score 0 · Accepted Answer · answered Apr 04 '14 at 12:10

0

Some serious problems with your listproducts.php

You should do this assignment on a constructor

public $database = parent::connection(); //<--- This gave you a syntax error.

Like this...

  public $database;
    function __construct()
    {
     $this->database = parent::connection();
    }

Next thing comes your read() , you need to make use of $this keyword..

Should be..

public function read(){
        $query = "SELECT name, price_in, price_out, category_products_id FROM products";
        $data = $this->database->query($query);   //<---- Do this way..

The fixed code..

<?php
require_once('initializing.php');

class DbPlus extends MySQLDatabaseConnection{

    public $database;
    function __construct()
    {
     $this->database = parent::connection();
    }

    public function read(){
        $query = "SELECT name, price_in, price_out, category_products_id FROM products";
        $data = $this->database->query($query);

        while ( $row = $data->fetch_object()) {
            echo $row->name;
        }
    }

}

$dbplus = new DbPLus;
$dbplus->read();

answered Apr 04 '14 at 12:10

Shankar Narayana Damodaran

68,075
43
96
126

1

Reference from the [PHP docs](http://www.php.net/manual/en/language.oop5.properties.php): `This declaration may include an initialization, but this initialization must be a constant value--that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated. ` – Mark Baker Apr 04 '14 at 12:12
Thanks for that Mark , It gave a parse error as the line of code was outside of the `constructor`, so that must be run-time related right ? – Shankar Narayana Damodaran Apr 04 '14 at 12:19
The fact that it needs to ___execute___ `parent::connection();` to get the value to assign means that it needs run-time information in order to be evaluated – Mark Baker Apr 04 '14 at 12:21
Thank you Mark , Any idea why was my answer downvoted ? – Shankar Narayana Damodaran Apr 04 '14 at 12:23
So Im a beginner, but if I got the point, parent::connection() should be executed, because it returns the connection, right? – jeugen Apr 04 '14 at 12:25
@user3497923, The first comment on this answer by Mark explains why you got a parse error. Yeah you are right `parent::connection()` returns you the connection. – Shankar Narayana Damodaran Apr 04 '14 at 12:27
2

@ShankarDamodaran - no idea why the downvote, I countered it by upvoting – Mark Baker Apr 04 '14 at 12:42
I didnt downvoted your answer, but I tried to upvote, but I dont have enough reps. Simple assignment public $database = parent::connection(); wont execute the method? – jeugen Apr 04 '14 at 12:48
Once again I have to say :) The answer lies in this [**comment**](http://stackoverflow.com/questions/22862399/how-can-i-use-variable-from-class-in-another-class/22862446?noredirect=1#comment34879576_22862446) by Mark. Let know if you find difficulty understanding it. – Shankar Narayana Damodaran Apr 04 '14 at 12:50
@ShankarDamodaran thank you for helping. Can you explain me, why cant I use **global $database;** inside the **DbPlus class** however I defined in the _initializing.php_ ? – jeugen Apr 04 '14 at 12:51
Because that breaks your `OOP` , Also , the singleton pattern you have used is a bad practice. Please read this beautiful article. http://tomnomnom.com/posts/why-global-state-is-the-devil-and-how-to-avoid-using-it – Shankar Narayana Damodaran Apr 04 '14 at 12:56
@ShankarDamodaran Thank you, I will carefully read it, and make some practice. Do you have any idea(article, link['same_as_above'], book) how to keep alive db connection when with oop, without usin singleton? Thank you again – jeugen Apr 04 '14 at 13:03
You need to look up on [**Persistent Database Connections**](http://www.php.net/manual/en/features.persistent-connections.php#features.persistent-connections) – Shankar Narayana Damodaran Apr 04 '14 at 13:07

score 0 · Answer 2 · answered Apr 04 '14 at 12:15

0

try something like this and let me know :

$dbplus = new DbPLus();
$dbplus->read();

Also give us the PHP version you are using

answered Apr 04 '14 at 12:15

Su4p

865
10
24

The parenthesis doesn't matter :) – Shankar Narayana Damodaran Apr 04 '14 at 12:17

How can I use variable from class in another class

2 Answers2

The fixed code..