protected function initKeys($constraints = '', $joins = '', $sorting = '')
    {
        $this->items = [];

        $query = implode(' ', [
            'SELECT t0.`'
            . $this->adapter->getSchema($this->table, 'primary')
            . '` FROM', '`'
            . $this->table
            . '` AS t0'
        ]);

        $rows = $this->adapter->getDriver()->query($query . $joins . $constraints . $sorting)->fetchAll();

        if (is_array($rows)) {
            $this->items = array_flip($rows);
        }
    }