BaseModel.php

<?php

class BaseModel implements ArrayAccess {

	public $attributes = array();

	public $attributes_cast_as = array(); // key => closure returning the value
	public $attributes_cast_as_integer = array();
	public $attributes_cast_as_float = array();
	public $attributes_cast_as_string = array();

	public function __isset($key)
	{
		return array_key_exists($key, $this->attributes);
	}


	public function __unset($key)
	{
		if ( array_key_exists($key, $this->attributes) ) {
			unset( $this->attributes[$key] );
		}
		return true;
	}


	public function __set($key, $value)
	{

		$value = $this->__castValue($key, $value, 'set');

		if ( is_array($value) )
			$value = json_encode($value);

		if ( array_key_exists($key, $this->attributes) ) {
			$this->attributes[$key] = $value;
		}

		return true;
	}


	public function __get($key)
	{

		if ( array_key_exists($key, $this->attributes) ) {
			$data = $this->attributes;
		}

		if ( !isset($data[$key]) )
			return null;

		$value = $data[$key];

		if ( $value instanceof Closure )
			$value = $value($this, $key, 'get');

		if ( is_scalar($value) ) {
			$json_value = json_decode($value, true);
			if ( is_array($json_value) ) {
				$json_value = $this->__castValue($key, $json_value, 'get');
				return $json_value;
			}
		}

		$value = $this->__castValue($key, $value, 'get');

		return $value;
	}


	public function __castValue($key, $value, $action = 'get') {

		if ( is_null($value) )
			return $value;

		if ( in_array($key, $this->attributes_cast_as_integer) )
			return intval($value);

		if ( in_array($key, $this->attributes_cast_as_float) )
			return floatval($value);

		if ( in_array($key, $this->attributes_cast_as_string) )
			return strval($value);

		if (
			!array_key_exists($key, $this->attributes_cast_as)
			||
			( array_key_exists($key, $this->attributes_cast_as) && !$this->attributes_cast_as[$key] instanceof Closure )
		)
			return $value;

		return $this->attributes_cast_as[$key]($value, $this, $action);
	}

	public function offsetSet($key, $value)
	{
		return $this->__set($key, $value);
	}


	public function offsetExists($key)
	{
		return $this->__isset($key);
	}


	public function offsetUnset($key)
	{
		$this->__unset($key);
	}


	public function offsetGet($key)
	{
		return $this->__get($key);
	}

	public function toArray() {
		$output = array();
		foreach ($this->attributes as $key => $value) {
			$value = $this->__get($key);
			$output[$key] = ( is_object($value) ) ? $value->toArray() : $value;
		}
		return $output;
	}

	public function toJson() {
		return json_encode($this->toArray());
	}

}

ChildModel.php

<?php

class ChildModel implements BaseModel {

	public $attributes = array(
		'id' => 0,
		'title' => '',
		'date' => '0000-00-00 00:00:00',
		'sample_custom' = '',
	);

	public function __construct(array $data = array()) {

		// Cast attribute "id" as integer
		$this->attributes_cast_as_integer[] = 'id';

		// Cast attribute "title" as string
		$this->attributes_cast_as_string[] = 'title';

		// Set "date" attribute value as current date
		if ( !isset($attributes['item_date']) )
			$this->__set('date', date('Y-m-d H:i:s'));

		// Custom attribute processing with a closure
		$this->attributes_cast_as['sample_custom'] = function($value, $object, $action) {
			if ( empty($value) && $action === 'set' )
				return 'Prepended string with id following:'.$object->id;
			return $value;
		};

		// Process any input attributes cast them and add them to the attributes property 
		foreach ($data as $key => $value) {
			$this->__set($key, $value);
		}

	}

}