Clarify a line/s --> setting sql data into object variables - php

Question

This is my first question here and I will try to clarify it as much as possible.
I am a begginer and I am going through lynda - beyond PHP MySQL lessons when I got to this part.
Code is working just fine, I just need better explanation for myself to the line that is commented in a code.
require_once('database.php');
class User {
public $id;
public $username;
public $password;
public $first_name;
public $last_name;
public static function find_all() {
return self::find_by_sql("SELECT * FROM users");
}
/////
public static function find_by_sql($sql="") {
global $database;
$result_set = $database->query($sql);
$user_array = array();
while ($row = $database->fetch_array($result_set)) {
$user_array[] = self::instantiate($row);
}
return $user_array;
}
And finaly lines that i almost understand :)
private static function instantiate($row) {
$user = new self;
foreach($row as $attribute=>$value){
if($user->has_attribute($attribute)) {
$user->$attribute = $value; /// THIS LINE BUGS ME
}
}
return $user;
}
private function has_attribute($attribute) {
$user_vars = get_object_vars($this);
return array_key_exists($attribute, $user_vars);
}
}
So I think I don't understand array_key_exists which returns TRUE or FALSE, in my case its true, but then line $users->$attributes =$value ; makes no sense for me,
So, I check if keys from fetch array MATCH variable names from object,
if($user->has_attribute($attribute)) { //and then this is true,perform nxt line
$user->$attribute = $value; // i got match of attribute above,how does it put values in $user_vars???
I know it says something like " if user has same attribute as key from that fetch array then put into that same attribute value of that attribute $value but i just dont see how it is done when i never returned object variables
Thank you for your time !
edit:
class variables names are equal to names of column_names from database

Answer 1

The User class has public attributes $id, $username, $password, etc. That means that you can assign values to the attributes in the following form:
$u = new User;
$u->id = 123;
$u->username = 'username';
and using dynamic property names:
$prop = 'id';
$u->$prop = 123;
$prop = 'username';
$u->$prop = 'username';
This is just the thing that happens in the lines that you don't understand:
if ($user->has_attribute($attribute)) {
$user->$attribute = $value;
The has_attribute method fetches all attributes of the $user object with get_object_vars function. The latter fetches the object properties as an array:
$user_vars = get_object_vars($this);
/* i.e.
$user_vars = array (
'id' => ...,
'username' => ...,
...
);
*/
Then the has_attribute method checks if the given $attribute key exists in the array of properties:
return array_key_exists($attribute, $user_vars);
If it exists (true), the $attribute property is assigned to $value.