Question

EDIT: I got this working now. I have updated the code:

I’ve looked at a few examples in here, and they all look logical. But I can’t get it to work. I have a class that extends my Data Access Layer (DAL). I would like to call parent class to retrieve DB results. What am I doig wrong?

DAL class

class DAL { 
  protected $username;     // the username for db connect 
  protected $pwd;          // the pwd to use when connecting 
  protected $host;         // the host to which one connects 
  protected $dbname;       // the db to select 
  public $conn;          // reference to the db link resource 
  public $db;            // result of db_select 
  public $query_result;  // the stored result of the last query you ran 

  public function __construct() 
  { 
    $this->username     = ""; 
    $this->pwd          = ""; 
    $this->host         = ""; 
    $this->dbname       = ""; 
  } 

  public function connect() 
  { 
    /* connects to DB here */
  }  

  private function query($sql) 
  {
    /* Executes the query here and stores the result in $this->query_result */
  }

  public function getAllCountries()
  {
    $sql =" 
      SELECT id, name
      FROM country";

    //Process query
    $this->query($sql);

    if($this->query_result)
      return $this->query_result;      
  }
}

And this is my other class

class myOtherClass extends DAL{

  public function __construct() {
   parent::__construct();
   parent::connect();
  }

  public function getCountryListBox()
  {
    $result = parent::getAllCountries();

    if($result)
    {
      $selectbox = "<select id='countryListBox' name='countryListBox'>";

      while ($row = mysql_fetch_array($result))
      {
        $selectbox .= "<option value='".($row['id'])."'>".($row['name'])."</option>";
      }
      $selectbox .= "</select>";
    }
    else
      $selectbox = "Countries could not be retrievd from database.";

    return  $selectbox;    
  }  
}

This is the code in my template:

$sl = new myOtherClass();

echo '<form id="label_data_form">';
  $sl->getCountryListBox(); 
echo '</form>';

Answer 1

The difference between these:

// $result = parent::getAllCountries();  // Like this
$result = this->getAllCountries();       // Or like this?

.. is probably best explained here:

class SuperFoo {
    function fubar () {
        echo "superfoo!";
    }

    function fuz () {
        echo "superfuz!";
    }
}

class SubBar extends SuperFoo {
    function fubar() {
        echo "subbar!";
    }

    function demonstrate() {
        $this->fubar();    // "subbar!"
        parent::fubar();   // "superfoo!"

        $this->fuz();      // "superfuz!"
        parent::fuz();     // "superfuz!"
    }
}

$s = new SubBar();
$s->demonstrate();

(okay, maybe not best explained..)

Unless you particularly want the behaviour defined in the parent class, I’d always use $this->... since then you have the option of altering the behaviour if needed.

---

The MySQL error seems to be caused by a problem with your SQL – the class inheritance looks to be working fine.