Passing attributes from one method to another in PHP

Question

I'm trying out classes and PHP:PDO. I've set up a simple class to try out some stuff but I'm getting an error "Undefined variable: conn" error.

class Cms {

    function __construct() {
        try {
            $conn = new PDO('mysql:host=localhost;dbname=blog', 'root', '');
            $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        } catch(PDOException $error) {
            echo 'error: ' . $error->getMessage();
        }
    }

    public function read() {
        $query = $conn->query("SELECT * FROM posts");
    }
}

To my knowledge this is probably because the $conn PDO object is not being passed onto the read method because it's being set in the construct method. What is the best(proper) way to let the read method be able to use the $conn attribute?

zerkms · Accepted Answer · 2013-03-17 20:26:49Z

5

class Cms {

    private $_conn;

    function __construct() {
        try {
            $this->_conn = new PDO('mysql:host=localhost;dbname=blog', 'root', '');
            $this->_conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        } catch(PDOException $error) {
            echo 'error: ' . $error->getMessage();
        }
    }

    public function read() {
        $query = $this->_conn->query("SELECT * FROM posts");
    }
}

So you create a private property, assign your PDO instance to it and use

Some documentation: http://www.php.net/manual/en/language.oop5.properties.php

answered Mar 17, 2013 at 20:26

zerkms

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2 Comments

Stephan de Vries Over a year ago

That works, couple questions though. 1. Is this considered best practice? 2. Why use private? I'm not that familiar with visiblity yet, is this a case of "When i'm not using the $conn property outside the class might aswell make it private?".

zerkms Over a year ago

@Stephan de Vries: 1. yep 2. because you don't want your class data to be changed without your permission

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