Classes Problem

thephplearner

I am trying to move from procedural to oop programming and having a few problems!!

Firstly I have a include with all my database connection details:

//setup connection information and place into variables for reuse later.
$db_address		= "XXXXXXXX";
$db_username	= "XXXXXXXXXXXX";
$db_passsword	= "XXXXXXXXXXX";
$db_name 		= "XXXXXXXXXX";
//test the database connection.
$db_connection 	= @mysql_connect($db_address,$db_username,$db_passsword) or die("Couldn't Connect.");
//test there is a database.
$db_select 		= @mysql_select_db($db_name,$db_connection) or die("Couldn't select database.");

Then I have a file where i am trying to write a class to extract info from my table:

include ("dbconnector.php");
class db_control
{ 
    var $dbconnection;        

	var $table;			//table that we will select from
	var $sql;			//query
    var $row;
	var $result; 

function selectInfo ()
	{
		$this->dbconnection = $db_connection;
		$this->sql = "SELECT * " .
		"FROM ".$this->table." ";
		$this->result = mysql_query($this->sql,$this->dbconnection)
		or die('Could not get connect to database; ' . mysql_error());
		$this->row = mysql_fetch_array($this->result); 	
	}	
}

Then I try to call the class:

$contact_details = new db_control();
$contact_details->table = 'contact_details';
$email = $contact_details->row['contact_email'];
echo "<p>$email</p>";

I have no idea where im going wrong :queasy:

quicknik

hi,

$db_connection isn't accessable by function selectInfo()
you need to call $contact_details->selectInfo()

bye,
nik

thephplearner

Sorry to be dumb, but how do i do this?!

quicknik

hi,
all vars from dbconnector.php are not seen by selectInfo () cause they are in globals scope.
you have eigther to import them to local scope by using the global directiv.
or setting the corresponding attributes after creating an instance of db_control.
Another (cleaner) way would be to use a constructor to initialize all attributes...
bye,
nikolas

thephplearner

am i getting any closer 😕

include ("dbconnector.php");
class db_control
{ 
    var $dbconnection;        // Tracks Database Connection 
	var $table;			//table that we will select from
	var $sql;			//query
    var $row;
	var $result; 

function selectInfo ()
	{
		$this->sql = "SELECT * " .
		"FROM ".$this->table." ";
		$this->result = mysql_query($this->sql,$this->dbconnection)
		or die('Could not get connect to database; ' . mysql_error());
		return $this->row = mysql_fetch_array($this->result); 	

	}	
}


$contact_details = new db_control();
$contact_details->select_info;
$contact_details->dbconnection = $db_connection;
$contact_details->table = 'contact_details';
$email = $contact_details->row['contact_email'];
echo "<p>$email</p>";

quicknik

try this ....

 include ("dbconnector.php");
class db_control
{ 
    var $dbconnection;        // Tracks Database Connection
    var $table;            //table that we will select from
    var $sql;            //query
    var $row;
    var $result; 

function selectInfo ()
    {
        $this->sql = "SELECT * " .
        "FROM ".$this->table." ";
        $this->result = mysql_query($this->sql,$this->dbconnection)
        or die('Could not get connect to database; ' . mysql_error());
        return $this->row = mysql_fetch_array($this->result);     

    }    
}
$contact_details = new db_control();
$contact_details->dbconnection = $db_connection;
$contact_details->table = 'contact_details';
$contact_details->select_info();
$email = $contact_details->row['contact_email'];
echo "<p>$email</p>";

things to keep in mind:
step 1. create an instance of your object
step 2. set neccesary attributes
step 3. execute needed methods.

it's also possible and probably better to use the constructor to set all init attributes...but first try to get it run in your version and then lets have a look and do some improvements 😉

bye,
niko

thephplearner

I'm getting an error saying im calling an undefined function 😕

bailo81

In the class the function name is defined as selectInfo but it is being called in the code as select_info

thephplearner

I just noticed that! Thanks for this, and a big thanks to Niko. I'm still a long way from understanding this properly but your code has really helped!!

quicknik

hi,

sorry i overlooked the typo...
here are few things that might help you to get a better understandig of what oop/classes is/means.
Classes/objects are to understand as a sort of construction plan. They consists of
attributes and methodes. Instances could be imagine as things build from this contruction plan. Of course you can use one construction plan to build as many things as you want.

Example:
Let's create a contrution plan of a car. It should hold the attributes
color, horsepower, mileage, manufacturer. And it should be able to drive
forward and backward.

class car {
    var $color;
    var $horsepower;
    var $mileage;
    var $manufacturer;

function drive_forward ($m)  {
           $this->mileage=$this->mileage + $m;
}

function drive_backward($m) {
           $this->mileage=$this->mileage - $m; // ;)
}

}

Now as we got a contrution plan we start assembling a few of our cars:

$mycar=new car();
$mycar->color='black';
$mycar->horsepower=380;
$mycar->mileage=10000;
$mycar->manufacturer='FORD';
$mycar -> drive_forward(100);
echo $mycar->mileage;

$mygirlfriendscar=new car();
$mygirlfriendscar->color='pink';
$mygirlfriendscar->horsepower=35;
$mygirlfriendscar->mileage=600000;
$mygirlfriendscar->manufacturer='VW';
$mygirlfriendscar -> drive_backward(100);
echo $mygirlfriendscar->mileage;

A more elegant way is to use a initialising constructor to set the attributes ...i will explain this later on if you are interested...

bye,
Nikolas

thephplearner

Thanks Niko,

This is a really good example. A lot of examples show how to construct the classes but not how to initiate the classes properly.

I would like to learn about initiating constructors too if you could help

quicknik

ok here we go:

first of all : php handles constructors different depending on the php version you are using but this only becomes interessting if you are using heredity. (i will explain that later if you are interessted).

A constructur is a special method which is executed automaticly if an instance is created (new car()).
So a constructor ist a good place to do some initializing stuff.
!! The constructor has to be of the same name as the class itself. !!

 class car {
    var $color;
    var $horsepower;
    var $mileage;
    var $manufacturer;

function car($c,$h,$m,$ma) {
         $this  -> color=$c;
         $this -> hosepower=$h;
         $this -> mileage=$m;
         $this -> manufacturer=$ma;
}

function drive_forward ($m)  {
           $this->mileage=$this->mileage + $m;
}

function drive_backward($m) {
           $this->mileage=$this->mileage - $m; // ;)
}

}

as you can see it becomes more clear:

$mycar=new car('black',380,10000,'FORD');
$mycar -> drive_forward(100);
echo $mycar->mileage;

$mygirlfriendscar=new car('pink',35,600000,'VW');
$mygirlfriendscar -> drive_backward(100);
echo $mygirlfriendscar->mileage;

got it?

cheers,
NIkolas

thephplearner

I think i do, im going to have a lot of fun playing round with this!

You have a good technique for writing examples Niko

Thanks again

quicknik

hi there,

i strongly recommend you to spend some time on playing around with other oop features like heredity and polymorphy.
Feel free to ask if you get stuck...
bye,
Nikolas

thephplearner

Thanks for this, i have been having a bit of a play and think maybe i should buy a book to help me along the way, any suggestions?

bailo81

For a good intro to OOP i'd totally recomment Sitepoints "The PHP anthology, object oriented PHP solutions, Volume 1

quicknik

are you thinking about a book regarding php or regarding oop?
me personal i, don't like learning from books.

regards,
nikolas