How to implement PDO FETCH_CLASS in correct way? - php

Question

Hi world genius of programming. I am quite newbie in PDO and OOP, Please understand.
I try to do the most simple thing in the world - get data from a table in MySQL.
I want to:
1) SELECT * from ... it's about 20 fields.
2) To get an array of object with 4-6 of properties.
3) I want to use fetchAll and FETCH_CLASS...
PDOStatement PDO::query ( string $statement , int $PDO::FETCH_CLASS , string $classname , array $ctorargs )
I've found that we can pass an array of argument but can't implement it.
So what am I doing?
class handler{
connection etc..
public $params = array('surname','id','country','display' );
return $stmt->fetchAll(PDO::FETCH_CLASS | PDO::FETCH_PROPS_LATE, 'person',$this->params);
class person {
public $surname=null;
public $id=null;
public $country=null;
public $status=null;
and then
__construct ()
i will not put it - cause i ve got 50 variants of them(((
}
So, I need to filter options from 20 fields fetching a class but not in SELECT mode instead of *...
Is it possible?
I know that you are genius!
Forgive for newbieness
UPDATE
function __construct($surname,$id,$country,$display) {
$this->surname=$surname;
$this->country=$country;
$id->id->$id
// that the only i need in this oblject
}
function __construct() {
$arg=array('surname','id');
foreach ($arg as $val) {
$this->{$val}=$$val;
}
}
it seems it maybe the next.. not construct function that will filter properties...
UPDATE
I tried solutions as #GolezTrol kindly proposed.
Solution 1 is arguing for... Notice: Undefined property: Person::$_attributes in
if i make
class Entity {
public $_attributes;
function __construct() { ....
or
class Person extends Entity {
public $_attributes;
}
it works.. but i get an object...
[0] => Person Object
(
[_attributes] => Array
(
[0] => surname
[1] => id
[2] => country
[3] => status
)
[id] => 298
.. it's not good(

Answer 1

I think you mean that you want to load only the properties that you specified instead of all values that were returned from the query. Your attempt is to do that by passing the desired field names to the constructor.
Solution 1: Just specify the array of properties and block the rest
Your way might just work, if you get a little help from the __set magic method. Using func_get_args() you can get all the arguments of a function (the constructor in this case) into an array. This way, you get the array of field names that you passed to fetch_all.
The magic setter only sets the properties if they exist in the array that was given to the constructor, so essentially it filters out all fields you don't want.
Advantage: easy. No specific implementation needed in descendant classes. You could just use Entity as a class for all entities.
Disadvantage: magic setter is called for every property and calls in_array this may be slow. fetch_all is determining which fields to read, while maybe this should be the class's responsibility.
class Entity {
function __construct() {
$this->_attributes = func_get_args();
}
function __set($prop, $value) {
if (in_array($prop, $this->_attributes)) {
$this->$prop = $value;
}
}
}
// If you would need a descendant class to introduce methods, you can..
class Person extends Entity {
}
$stmt->fetchAll(PDO::FETCH_CLASS | PDO::FETCH_PROPS_LATE, 'Person', array('id', 'surname', 'gender'))
Solution 2: block all properties that don't exist
Similar solution, but much cleaner, I think. Implement the magic setter and make it do... nothing. It will be called for properties that don't exist and only for properties that don't exist. So in Person you just declare whatever values you want to read. All other properties will be directed to the empty __set method so they are implicitly ignored.
Advantage: Still easy. Hardly any implementation. You can put the empty method in a base class or just implement it in Person and every other class you have. You just declare the properties in Person. You don't even need to specify the fields you want to read in fetch_all. Also, reading into existing properties is faster.
Disadvantage: if you want to read different sets of information into the same class, this is not possible. The person in my example below always has an id, surname and gender. If you want to read for instance id only, you have to introduce another class. But would you want that?..
class Entity {
function __set($prop, $value) {
// Ignore any property that is not declared in the descendant class.
}
}
class Person extends Entity {
public $id = null;
public $surname = null;
public $gender = null;
}
$stmt->fetchAll(PDO::FETCH_CLASS | PDO::FETCH_PROPS_LATE, 'Person')
Solution 3: Read only the fields you want
This is actually the best solution. Instead of selecting all fields, SELECT *, select only the fields you want to have: SELECT id, surname, gender ... This way, you won't have objects with too many values, but more importantly, you also decrease the load on your database. The database doesn't need to fetch the data, PHP doesn't need to receive it, and if the database server is separate from the webserver, you also save network traffic. So in all regards, I think this is the best option.