php - Scope error - Call to a member function prepare() on a non-object

So the scenario is simple. I use class that does something in database but in that class I call another class that also does something in DB.

Thanks, include_once changed to include and it works!

This is what I get:

Fatal error: Call to a member function
prepare() on a non-object -> mLog.php on line 20

I use db_config.php to create PDO object and then include it in my classes.

db_config.php

try

{
    $DBH = new PDO("mysql:host=$db_host;dbname=$db_name", $db_user, $db_pass);

    $DBH->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);
}
catch (PDOException $e)
{
    echo $e->getMessage();
}

1st class mLog.php

    class Log
    {
        public static function Add($action)
        {
            try

            {
                include_once "db_config.php";

                $ip = $_SERVER['REMOTE_ADDR'];

                $time = date('Y-m-d');

                $values = array($ip, $action, $time);
//ERROR NEXT LINE
                $STH = $DBH->prepare("INSERT INTO log (ip, action, time)

                                      VALUES (?, ?, ?)");

                $STH->execute($values);

                $DBH = null;
                $STH = null;
            }
            catch (PDOException $e)
            {
                echo $e->getMessage();

            }
        }
    }

second class that uses first class (fragment because it's big and has many functions)

public static function Add($catName, $catDescr = "", $catImgURL = "", $catSubLevel = 0, $catSubID = 0)
{
    try

    {
        include_once "db_config.php";
        include_once "mLog.php";

        $values = array($catName, $catDescr, $catImgURL, $catSubLevel, $catSubID);
        $STH = $DBH->prepare("INSERT INTO cat (catName, catDescr, catImg, catSubLevel, catSubID)
                              VALUES (?, ?, ?, ?, ?)");

        $STH->execute($values);


        $DBH = null;
        $STH = null;

        //HERE IT IS
        Log::Add("Added category 111" . $catName);

        return true;
    }
    catch (PDOException $e)
    {

        echo $e->getMessage();
    }
}

Answer

You used include_once "db_config.php"; instead of include "db_config.php";.

As I understand from your code, each time you include db_config.php, you will create the database object $DBH.

Since you put it as include_once, it will only run db_config.php once, and in the log class when you try to include it, it will not run - since it has already been included in the Add method.

To improve on this, you should create a class that solely manages (or encapsulate) the PDO object. You can simply create a Singleton class that returns the PDO object, include the class once at the top, and fetch the object where ever you are in the code.

Example:

DBAccess.php

class DBAccess extends Singleton{

    // there is a getInstance() method in the Singleton abstract class


    private $dbh;

    // The PDO object is created only once when the first getInstance() is called in Singleton.
    function __construct(){
        try
        {
            $this->dbh = new PDO("mysql:host=$db_host;dbname=$db_name", $db_user, $db_pass);

            $this->dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);

        }
        catch (PDOException $e)
        {
            echo $e->getMessage();
        }

    }

    /**
     * Get the PDO object

     * @return object
     */
    public static function getDBH(){
        return self::getInstance()->dbh;
    }

}

Log Class:

class Log
{
    public static function Add($action)
    {
        try
        {
            $DBH = DBAccess::getDBH();

            $ip = $_SERVER['REMOTE_ADDR'];


            $time = date('Y-m-d');

            $values = array($ip, $action, $time);

            $STH = $DBH->prepare("INSERT INTO log (ip, action, time)
                                  VALUES (?, ?, ?)");

            $STH->execute($values);
        }

        catch (PDOException $e)
        {
            echo $e->getMessage();
        }
    }
}

Usage:

include_once('db_config.php');
include_once('mLog.php');

public static function Add($catName, $catDescr = '', $catImgURL = '', $catSubLevel = 0, $catSubID = 0)
{
    try
    {

        $DBH = DBAccess::getDBH();


        $values = array($catName, $catDescr, $catImgURL, $catSubLevel, $catSubID);

        $STH = $DBH->prepare("INSERT INTO cat (catName, catDescr, catImg, catSubLevel, catSubID)
                              VALUES (?, ?, ?, ?, ?)");

        $STH->execute($values);

        $DBH = null;

        Log::Add("Added category 111" . $catName);


        return true;
    }
    catch (PDOException $e)
    {
        echo $e->getMessage();
    }
}