PHP inheritance concerning mysqli

Question

I've created a class named Database.

class Database extends mysqli {

    public function __construct() {
        parent::__construct();
        $mysqli = new mysqli(DBHOST, DBUSER, DBPASSWORD, DBDATABASE);

        if (mysqli_connect_errno()) {
            printf("Connect failed: %s\n", mysqli_connect_error());
            exit();
        }
    }   
}

And a class called Model that extends Database

class Model {

    function __construct() {
        $this->db = new Database();        
    }
}

And a class registerModel that extends Model

class registerModel extends Model {

    public function __construct() {
        echo "This is the register Model";
    }

    public function register(//VARIOUS PASSED VALUES) {
        **$stmt = $mysqli->prepare("INSERT INTO users (firstName, lastName) values (?, ?)");**
        ...
        ... More Code
        ...

    }

What I'm trying to do is get the $mysqli from the original Database class, but I'm unsure how to refer to it. I've tried everything, but nothing seems to work.

P.S. The first two classes are always required in my application, and the last registerModel class is called via a controller. Which is why I don't construct the parent in the sub-classes.

A suggestion: don't create classes with new() inside the constructor, pass them as an argument from the outside instead. — Aditya M P
– Aditya M P, Commented Dec 16, 2012 at 0:15

Ry- · Accepted Answer · 2012-12-16 00:13:41Z

2

Make it a field inside the Database class:

class Database extends mysqli {
    public $mysqli;

    public function __construct() {
        parent::__construct();
        $this->mysqli = new mysqli(DBHOST, DBUSER, DBPASSWORD, DBDATABASE);

        if (mysqli_connect_errno()) {
            printf("Connect failed: %s\n", mysqli_connect_error());
            exit();
        }
    }   
}

Then you can refer to it like so:

$stmt = $this->db->mysqli->prepare("INSERT INTO users (firstName, lastName) values (?, ?)");

But you also need to keep the parent constructor:

echo "This is the register Model";
parent::__construct();

Finally, your Database class shouldn't extend mysqli, because you don't actually use that inheritance; you're creating a completely different object.

answered Dec 16, 2012 at 0:13

Ry-♦

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2 Comments

christopher Over a year ago

This will not work because __construct in registerModel will override the __construct in Database

AlexHeuman Over a year ago

Ahhh, I see. I was putting '$' variable markers where I didn't need to. Thank you very much for your help.

Wing Lian · Accepted Answer · 2012-12-16 00:14:25Z

2

In your register model, the constructor needs to call the parent constructor

<?php
class registerModel extends Model {
public function __construct() {
    echo "This is the register Model";
    parent::__construct();
}

And then you can access it from

$this->db

answered Dec 16, 2012 at 0:14

Wing Lian

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2 Comments

christopher Over a year ago

This will work. It overrides the __construct, but it calls the parent::__construct() to get the variable $mysqli

AlexHeuman Over a year ago

Thank you very much, I was putting dollar signs like this $this->$db when I shouldn't have. Thank you for your answer.

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