Db.php

<?php

namespace Db;

class Db {
	private $connection;

	public function __construct(\PDO $connection) {
		$connection->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);

		$this->connection = $connection;
	}

	public function create(DbModel $model) {
		if (! $model->isNew()) {
			throw new DbException("Can't create NOT NEW model.");
		}

		$data = $model->getData();

		$columns = [];
		$params = [];
		$defered = [];

		foreach ($data as $attr => $value) {
			if (is_array($value)) {
				foreach ($value as $valueModel) {
					$this->save($valueModel);
				}
			} else if (is_object($value)) {
				$defered[] = $value;
			} else {
				$columns[] = $attr;
				$placeholder = ':' . $attr;
				$params[$placeholder] = $value;
				$placeholders[] = $placeholder;
			}
		}

		$sql = 'INSERT INTO ' . $model->getStoreName() . '(' . implode(', ', $columns) . ') VALUES(' . implode(', ', $placeholders) . ')';

		$sth = $this->connection->prepare($sql);

		if ($sth->execute($params) === false) {
			throw new DbException("Can't create model.");
		}

		$model->id = $this->connection->lastInsertId();

		if (count($defered) > 0) {
			foreach ($defered as $deferedModel) {
				$this->save($deferedModel);
			}
		}

		return true;
	}

	public function find($modelName, $sql='', array $params=array()) {
		$sql = 'SELECT tbl.* FROM ' . $modelName::getStoreName() . ' AS tbl ' . $sql;

		$sth = $this->connection->prepare($sql);

		$sth->setFetchMode(\PDO::FETCH_CLASS, $modelName);

		if ($sth->execute($params) === false) {
			return null;
		}

		return $sth->fetchAll();
	}

	public function findOne($modelName, $sql='', array $params=array()) {
		$sql = 'SELECT tbl.* FROM ' . $modelName::getStoreName() . ' AS tbl ' . $sql;

		$sth = $this->connection->prepare($sql);

		$sth->setFetchMode(\PDO::FETCH_CLASS, $modelName);

		if ($sth->execute($params) === false) {
			return null;
		}

		return $sth->fetch();
	}

	public function update(DbModel $model) {
		if ($model->isNew()) {
			throw new DbException("Can't update NEW model.");
		}

		$data = $model->getData();

		$pairs = [];
		$params = [];
		$defered = [];

		foreach ($data as $attr => $value) {
			if ($attr === 'id') {
				continue;
			}

			if (is_array($value)) {
				foreach ($value as $valueModel) {
					$this->save($valueModel);
				}
			} else if (is_object($value)) {
				$defered[] = $value;
			} else {
				$placeholder = ':' . $attr;
				$params[$placeholder] = $value;
				$pairs[] = $attr . '=:' . $attr;
			}
		}

		$sql = 'UPDATE ' . $model->getStoreName() . ' SET ' . implode(', ', $pairs) . ' WHERE id=:id LIMIT 1';
		$params[':id'] = $model->id;

		$sth = $this->connection->prepare($sql);

		if ($sth->execute($params) === false) {
			throw new DbException("Can't update model.");
		}

		if (count($defered) > 0) {
			foreach ($defered as $deferedModel) {
				$this->save($deferedModel);
			}
		}

		return true;
	}

	public function save(DbModel $model) {
		if ($model->isNew()) {
			$this->create($model);
		} else {
			$this->update($model);
		}
	}

	public function remove(DbModel $model) {
		if ($model->isNew()) {
			throw new Exception("Can't remove NEW model.");
		}

		$sql = 'DELETE FROM ' . $model->getStoreName() . ' WHERE id=:id'; 

		$sth = $this->connection->prepare($sql);

		$sth->bindValue(':id', $model->id, \PDO::PARAM_INT);

		if ($sth->execute() === false) {
			throw new DbException("Can't remove model.");
		}

		unset($model->id);

		return true;
	}
}

class DbException extends \Exception { }

DbModel.php

<?php

namespace Db;

abstract class DbModel {
	public $id;

	abstract public static function getStoreName();

	public function getAttrs() {
		return array_keys(get_class_vars(get_class($this)));
	}

	public function getData() {
		$attrs = $this->getAttrs();

		$data = [];

		foreach ($attrs as $attr) {
			if (isset($this->{$attr})) {
				$data[$attr] = $this->{$attr};
			} else {
				$data[$attr] = '';
			}
		}

		return $data;
	}

	public function setData(array $data) {
		$attrs = $this->getAttrs();

		foreach ($attrs as $attr) {
			if (isset($data[$attr])) {
				$this->{$attr} = $data[$attr];
			}
		}
	}

	public function isNew() {
		return empty($this->id);
	}
}

index.php

<?php

require_once('Db/Db.php');
require_once('Db/DbModel.php');
require_once('models/Order.php');
require_once('models/Product.php');

$connection = new PDO('mysql:dbname=dbtest;host=localhost', 'root', 'root');

$db = new \Db\Db($connection);

$product = new \models\Product;
$product->setData([
	'newAttr' => 'my attr',
	'name' => 'Another name',
]);

$order = new \models\Order;
$order->customer_name = 'Ivan';
$order->addProduct($product);

$db->save($order);

Order.php

<?php

namespace models;

class Order extends \Db\DbModel {
	public $customer_name;
	public $is_completed;
	public $products = array();

	public function isCompleted() {
		return $this->is_completed === '1' ? true: false;
	}

	public function addProduct(Product $model) {
		$this->products[] = $model;
		$model->order = $this;
	}

	public static function getStoreName() {
		return 'user_order';
	}
}

Product.php

<?php

namespace models;

class Product extends \Db\DbModel {
	public $name;
	public $price;
	public $image;

	public static function getStoreName() {
		return 'product';
	}
}