Getting the name of a child class in the parent class (static context)

Question

I'm building an ORM library with reuse and simplicity in mind; everything goes fine except that I got stuck by a stupid inheritance limitation. Please consider the code below:

class BaseModel {
    /*
     * Return an instance of a Model from the database.
     */
    static public function get (/* varargs */) {
        // 1. Notice we want an instance of User
        $class = get_class(parent); // value: bool(false)
        $class = get_class(self);   // value: bool(false)
        $class = get_class();       // value: string(9) "BaseModel"
        $class =  __CLASS__;        // value: string(9) "BaseModel"

        // 2. Query the database with id
        $row = get_row_from_db_as_array(func_get_args());

        // 3. Return the filled instance
        $obj = new $class();
        $obj->data = $row;
        return $obj;
    }
}

class User extends BaseModel {
    protected $table = 'users';
    protected $fields = array('id', 'name');
    protected $primary_keys = array('id');
}
class Section extends BaseModel {
    // [...]
}

$my_user = User::get(3);
$my_user->name = 'Jean';

$other_user = User::get(24);
$other_user->name = 'Paul';

$my_user->save();
$other_user->save();

$my_section = Section::get('apropos');
$my_section->delete();

Obviously, this is not the behavior I was expecting (although the actual behavior also makes sense).. So my question is if you guys know of a mean to get, in the parent class, the name of child class.

Answer 1

in short. this is not possible. in php4 you could implement a terrible hack (examine the debug_backtrace()) but that method does not work in PHP5. references:

• 30423

• 37684

• 34421

edit: an example of late static binding in PHP 5.3 (mentioned in comments). note there are potential problems in it's current implementation (src).

class Base {
    public static function whoAmI() {
        return get_called_class();
    }
}

class User extends Base {}

print Base::whoAmI(); // prints "Base"
print User::whoAmI(); // prints "User"

Answer 2

You don't need to wait for PHP 5.3 if you're able to conceive of a way to do this outside of a static context. In php 5.2.9, in a non-static method of the parent class, you can do:

get_class($this);

and it will return the name of the child class as a string.

i.e.

class Parent() {
    function __construct() {
        echo 'Parent class: ' . get_class() . "\n" . 'Child class: ' . get_class($this);
    }
}

class Child() {
    function __construct() {
        parent::construct();
    }
}

$x = new Child();

this will output:

Parent class: Parent
Child class: Child

sweet huh?

Answer 3

I know this question is really old, but for those looking for a more practical solution than defining a property in every class containing the class name:

You can use the static keyword for this.

As explained in this contributor note in the php documentation

the static keyword can be used inside a super class to access the sub class from which a method is called.

Example:

class Base
{
    public static function init() // Initializes a new instance of the static class
    {
        return new static();
    }

    public static function getClass() // Get static class
    {
        return static::class;
    }

    public function getStaticClass() // Non-static function to get static class
    {
        return static::class;
    }
}

class Child extends Base
{

}

$child = Child::init();         // Initializes a new instance of the Child class

                                // Output:
var_dump($child);               // object(Child)#1 (0) {}
echo $child->getStaticClass();  // Child
echo Child::getClass();         // Child

Answer 4

I know its old post but want to share the solution I have found.

Tested with PHP 7+ Use the function get_class()link

<?php
abstract class bar {
    public function __construct()
    {
        var_dump(get_class($this));
        var_dump(get_class());
    }
}

class foo extends bar {
}

new foo;
?>

The above example will output:

string(3) "foo"
string(3) "bar"

Answer 5

In case you don't want to use get_called_class() you can use other tricks of late static binding (PHP 5.3+). But the downside in this case you need to have getClass() method in every model. Which is not a big deal IMO.

<?php

class Base 
{
    public static function find($id)
    {
        $table = static::$_table;
        $class = static::getClass();
        // $data = find_row_data_somehow($table, $id);
        $data = array('table' => $table, 'id' => $id);
        return new $class($data);
    }

    public function __construct($data)
    {
        echo get_class($this) . ': ' . print_r($data, true) . PHP_EOL;
    }
}

class User extends Base
{
    protected static $_table = 'users';

    public static function getClass()
    {
        return __CLASS__;
    }
}

class Image extends Base
{
    protected static $_table = 'images';

    public static function getClass()
    {
        return __CLASS__;
    }
}

$user = User::find(1); // User: Array ([table] => users [id] => 1)  
$image = Image::find(5); // Image: Array ([table] => images [id] => 5)

Answer 6

It appears you might be trying to use a singleton pattern as a factory pattern. I would recommend evaluating your design decisions. If a singleton really is appropriate, I would also recommend only using static methods where inheritance is not desired.

class BaseModel
{

    public function get () {
        echo get_class($this);

    }

    public static function instance () {
        static $Instance;
        if ($Instance === null) {
            $Instance = new self;

        }
        return $Instance;
    }
}

class User
extends BaseModel
{
    public static function instance () {
        static $Instance;
        if ($Instance === null) {
            $Instance = new self;

        }
        return $Instance;
    }
}

class SpecialUser
extends User
{
    public static function instance () {
        static $Instance;
        if ($Instance === null) {
            $Instance = new self;

        }
        return $Instance;
    }
}


BaseModel::instance()->get();   // value: BaseModel
User::instance()->get();        // value: User
SpecialUser::instance()->get(); // value: SpecialUser

Answer 7

Maybe this isn't actually answering the question, but you could add a parameter to get() specifing the type. then you can call

BaseModel::get('User', 1);

instead of calling User::get(). You could add logic in BaseModel::get() to check whether a get method exists in the subclass and then call that if you want to allow the subclass to override it.

Otherwise the only way I can think of obviously is by adding stuff to each subclass, which is stupid:

class BaseModel {
    public static function get() {
        $args = func_get_args();
        $className = array_shift($args);

        //do stuff
        echo $className;
        print_r($args);
    }
}

class User extends BaseModel {
    public static function get() { 
        $params = func_get_args();
        array_unshift($params, __CLASS__);
        return call_user_func_array( array(get_parent_class(__CLASS__), 'get'), $params); 
    }
}


User::get(1);

This would probably break if you then subclassed User, but I suppose you could replace get_parent_class(__CLASS__) with 'BaseModel' in that case

Answer 8

The problem is not a language limitation, it is your design. Never mind that you have classes; the static methods belie a procedural rather than object-oriented design. You're also using global state in some form. (How does get_row_from_db_as_array() know where to find the database?) And finally it looks very difficult to unit test.

Try something along these lines.

$db = new DatabaseConnection('dsn to database...');
$userTable = new UserTable($db);
$user = $userTable->get(24);

Answer 9

Two variations on Preston's answer:

1)

class Base 
{
    public static function find($id)
    {
        $table = static::$_table;
        $class = static::$_class;
        $data = array('table' => $table, 'id' => $id);
        return new $class($data);
    }
}

class User extends Base
{
    public static $_class = 'User';
}

2)

class Base 
{
    public static function _find($class, $id)
    {
        $table = static::$_table;
        $data = array('table' => $table, 'id' => $id);
        return new $class($data);
    }
}

class User extends Base
{
    public static function find($id)
    {
        return self::_find(get_class($this), $id);
    }
}

Note: starting a property name with _ is a convention that basically means "i know i made this public, but it really should have been protected, but i couldn't do that and achieve my goal"