PHP Classes

irish12

I am just learning how to use classes. I understand it somewhat but I am having a little trouble here.
I have a class that makes the MYSQL connection, executes queries etc... and all works just fine there. I then created another class that extends the connection class but I can't get it to work.
It is a simple class that just retrieves a value from a database table.

class testextend extends mysql_database{
	var $connection;

function testextend($ID){
	$sql="
	Select 
		CatID
	From
		" . $this -> select_dbTable(Ad) ."
	Where
		AdID = '$ID'";
	$result = $this -> execute_query($sql);
	$row = $this->fetch_row_array($result);

	return $row["CatID"];
}
}

Here is the error that I get when I call this class on a webpage: Nonfatal Database Error: Unable to connect to database

On the webpage I include the class_database, include the testclass and then call the testclass like this:

 
$test2 = new testextend(2);
echo "test2 : ",$test2,"<br>\n";

Can anyone tell me where I am going wrong?

eoghain

PHP doesn't automatically call the base classes constructor, you will need to manually do that in your extended classes constructor:

class testextend extends mysql_database{
    var $connection;

function testextend($ID){
    parent::mysql_database();

    $sql="
    Select
        CatID
    From
        " . $this -> select_dbTable(Ad) ."
    Where
        AdID = '$ID'";
    $result = $this -> execute_query($sql);
    $row = $this->fetch_row_array($result);

    return $row["CatID"];
}
}

irish12

Thanks for your help, eoghain.

That worked. It did bring up some more questions though. I am passing in the database authentication via arguments so I actually had to write a constructor in the sub-class like this and I renamed the other method:

function testextend ($dbserver,$dbdatabase,$dbusername,$dbpassword){
	parent::mysql_database($dbserver,$dbdatabase,$dbusername,$dbpassword); 
	}

I also have other sub-classes with the same constructor. So when I call it from the webpage, will I have to call it like this:

 
$mydb = new mysql_database($dbserver,$dbdatabase,$dbusername,$dbpassword);
$html = new testextend ($dbserver,$dbdatabase,$dbusername,$dbpassword);
$tableinfo = new testextend2 ($dbserver,$dbdatabase,$dbusername,$dbpassword);

There must be a better way of doing this?

eoghain

Yes, the way you have it setup you will have to pass in all of that information for every class that extends your database connection.

Personally I don't extend my classes from my database class, I just give them a reference to it. Unless your sub-classes actually add more functionality to your database class there isn't any reason to extend it. But that's just how I view things.

irish12

eoghain,

What do you mean by "give them a reference to it"? do you mean, you would create an instance to the database class and then pass that reference in as an argument to the other classes?

For example, you would do something like this:

$mydb = new database_class();
$myhtml = new html_class($mydb);

and then I would be able to access all the methods of database_class() from html_class($mydb) via $this -> method?

eoghain

I would do basically what you show. I would create my database class that did the work I wanted (usually just process queries and return the data in a form that is useful to me). Then I'd pass the refernce to that class into my new class and assign it to a member and access it that way.

class myclass
{
   var $dbConn = null;

   function myclass($dbConn)
   {
      $this->dbConn = $dbConn
   }

   function getSomeData()
   {
      $sql = "SELECT * FROM Table";
      $this->dbConn->RunQuery($sql);
   }
}

Something like that.

irish12

Ahh yes, thanks a lot, eoghain