Method checkOut

/**
 * Method to check a row out if the necessary properties/fields exist.
 *
 * To prevent race conditions while editing rows in a database, a row can be checked out if the fields 'checked_out' and 'checked_out_time'
 * are available. While a row is checked out, any attempt to store the row by a user other than the one who checked the row out should be
 * held until the row is checked in again.
 *
 * @param   integer  $userId  The Id of the user checking out the row.
 * @param   mixed    $pk      An optional primary key value to check out.  If not set the instance property value is used.
 *
 * @return  boolean  True on success.
 *
 * @since   1.7.0
 * @throws  \UnexpectedValueException
 */
public function checkOut($userId, $pk = null)
{
    // Pre-processing by observers
    $event = AbstractEvent::create('onTableBeforeCheckout', ['subject' => $this, 'userId' => $userId, 'pk' => $pk]);
    $this->getDispatcher()->dispatch('onTableBeforeCheckout', $event);
    // If there is no checked_out or checked_out_time field, just return true.
    if (!$this->hasField('checked_out') || !$this->hasField('checked_out_time')) {
        return true;
    }
    if (\is_null($pk)) {
        $pk = array();
        foreach ($this->_tbl_keys as $key) {
            $pk[$key] = $this->{$key};
        }
    } elseif (!\is_array($pk)) {
        $pk = array($this->_tbl_key => $pk);
    }
    foreach ($this->_tbl_keys as $key) {
        $pk[$key] = \is_null($pk[$key]) ? $this->{$key} : $pk[$key];
        if ($pk[$key] === null) {
            throw new \UnexpectedValueException('Null primary key not allowed.');
        }
    }
    // Get column names.
    $checkedOutField = $this->getColumnAlias('checked_out');
    $checkedOutTimeField = $this->getColumnAlias('checked_out_time');
    // Get the current time in the database format.
    $time = Factory::getDate()->toSql();
    // Check the row out by primary key.
    $query = $this->_db->getQuery(true)->update($this->_tbl)->set($this->_db->quoteName($checkedOutField) . ' = ' . (int) $userId)->set($this->_db->quoteName($checkedOutTimeField) . ' = ' . $this->_db->quote($time));
    $this->appendPrimaryKeys($query, $pk);
    $this->_db->setQuery($query);
    $this->_db->execute();
    // Set table values in the object.
    $this->{$checkedOutField} = (int) $userId;
    $this->{$checkedOutTimeField} = $time;
    // Post-processing by observers
    $event = AbstractEvent::create('onTableAfterCheckout', ['subject' => $this, 'userId' => $userId, 'pk' => $pk]);
    $this->getDispatcher()->dispatch('onTableAfterCheckout', $event);
    return true;
}