Another useful feature is accessing your custom object collections as arrays in PHP. There are two interfaces available in PHP (>=5.0.0) core to support this: ArrayAccess and Iterator. The former allows you to access your custom objects as array.

ArrayAccess

Assume we have a user class and a database table storing all the users. We would like to create a UserCollection class that will:

1. allow us to address certain user by their username unique identifier
2. perform basic (not all CRUD, but at least Create, Retrieve and Delete) operations on our users collection

Consider the following source (hereinafter we’re using short array creation syntax [] available since version 5.4):

class UserCollection implements ArrayAccess {
    protected $_conn;
    
    protected $_requiredParams = ['username','password','email'];
    
    public function __construct() {
        $config = new Configuration();

        $connectionParams = [
            //your connection to the database
        ];
        
        $this->_conn = DriverManager::getConnection($connectionParams, $config);
    }
    
    protected function _getByUsername($username) {
        $ret = $this->_conn->executeQuery('SELECT * FROM `User` WHERE `username` IN (?)',
            [$username]
        )->fetch();
        
        return $ret;
    }
    
    // START of methods required by ArrayAccess interface
    public function offsetExists($offset) {
        return (bool) $this->_getByUsername($offset);
    }

    public function offsetGet($offset) {
        return $this->_getByUsername($offset);
    }

    public function offsetSet($offset, $value) {
        if (!is_array($value)) {
            throw new \\Exception('value must be an Array');
        }

        $passed = array_intersect(array_values($this->_requiredParams), array_keys($value));
        if (count($passed) < count($this->_requiredParams)) {
            throw new \\Exception('value must contain at least the following params: ' . implode(',', $this->_requiredParams));
        }
        $this->_conn->insert('User', $value);
    }

    public function offsetUnset($offset) {
        if (!is_string($offset)) {
            throw new \\Exception('value must be the username to delete');
        }
        if (!$this->offsetGet($offset)) {
            throw new \\Exception('user not found');
        }
        $this->_conn->delete('User', ['username' => $offset]);
    }
    // END of methods required by ArrayAccess interface
}

then we can :

$users = new UserCollection();

var_dump(empty($users['testuser']),isset($users['testuser']));
$users['testuser'] = ['username' => 'testuser', 
                      'password' => 'testpassword',
                      'email'    => '[email protected]'];
var_dump(empty($users['testuser']), isset($users['testuser']), $users['testuser']);
unset($users['testuser']);
var_dump(empty($users['testuser']), isset($users['testuser']));

which will output the following, assuming there was no testuser before we launched the code:

bool(true)
bool(false)
bool(false)
bool(true)
array(17) {
  ["username"]=>
  string(8) "testuser"
  ["password"]=>
  string(12) "testpassword"
  ["email"]=>
  string(13) "[email protected]"
}
bool(true)
bool(false)

IMPORTANT: offsetExists is not called when you check existence of a key with array_key_exists function. So the following code will output false twice:

var_dump(array_key_exists('testuser', $users));
$users['testuser'] = ['username' => 'testuser', 
                      'password' => 'testpassword',
                      'email'    => '[email protected]'];
var_dump(array_key_exists('testuser', $users));

Iterator

Let’s extend our class from above with a few functions from Iterator interface to allow iterating over it with foreach and while.

First, we need to add a property holding our current index of iterator, let’s add it to the class properties as $_position:

// iterator current position, required by Iterator interface methods
protected $_position = 1;

Second, let’s add Iterator interface to the list of interfaces being implemented by our class:

class UserCollection implements ArrayAccess, Iterator {

then add the required by the interface functions themselves: