Objects

[nightowl]

let's say you are building an application concerning cars and, since you want to create a solid and extendable application, you try to do so in an OO way. you define the object "car"

class car {} with several methods (changeColor, copy, ...)

Everything is of course stored in a database.

But what if you want to "list all cars" ... how do you go ahead? Normally: pg_query("select * from cars"); etc... But how do you do it in OO way ?

do you define a class "cars" ? do you create a method in "car" like "listAllCars" ? And if you choose for the class "cars", does it inherit from car or does car inherit from cars ? Or neither ?

[Shrike]

Create a class called Cars which is a container for instances of Car, and also contains a factory method for creating instances of Car from the database data. I think that's a pretty standard pattern 🙂

[nightowl]

hehe - I guess thanks. But I don't understand the first bit from it.

Could you please give some example code ? Or a pointer to a website? I've tried to google something up but couldn't find much.

[Shrike]

A simple example.

class Cars {
   var $cars = array();

   function add(&$car){
    $this->cars[] =& $car;
  }

  function factory($record){
    $car =& new Car($record);
    /* Any special processing of each car object could be done here */
    $this->add(&$car);
  }
  /* Some methods to show information about the cars */
  function list_cars(){}
  function sort_cars(){}
  function total_cars(){}
}

class Car {
  var $colour;
  var $number_of_wheels;

  function car($record){
    $this->colour = $record['colour'];
    $this->number_of_wheels = $record['number_of_wheels'];
  }
}

$cars = new Cars;
/* Assume there is some record set $carset */
foreach($carset as $car){
  $cars->factory($car);
}

[nightowl]

"/ Assume there is some record set $carset / "

This is kinda my initial question: isn't it the purpose that the cars-class generates this recordset? Or should every page using the cars class write it's own query ?

I was thinking of the following

class cars {
var $cars = array();

function cars (&$db) {
// where $db is an instance of my DBA layer ezSQL
// dunno how this could be improved but I don't feel
// at ease with this kind of passing around pointers
$this->db = $db;

}

function add(&$car) {

   $fields = get_object_vars($car);
   foreach ($fields as $field) {
        $values[$field] = $car->$field;
   } 

   $sql = "insert into cars (".implode (',', $fields).") values ('".implode ("','",$values)."')" ;
   $this->db->query($sql);

   $this->cars[] = $car;

}

funciton fetch_all() {

    $sql = "select * from cars";
    $this->cars = $this->db->get_results($sql);

}

function list_all() {
if (empty($this->cars)) {
$this->fetch_all();
}
return $this->cars;

}

}

So ... I would like to include my SQL statements in my classes. Is that a bad idea ? Should I set it up differently ?

Questions one never finds an answer to in articles around the internet. Or maybe I'm looking in the wrong place / for the wrong keywords

[Shrike]

Have a read of the design patterns at www.phppatterns.com. Some of them are quite advanced, but a few are easy to grasp and also in the same ball park as what you want to do (e.g. the second Factory pattern example is pretty much the one I used in the above example.)

[nightowl]

i hadn't found that site yet. Ill have a look. Thanks for the pointer!