public function filterByCountry($country, $comparison = null)
    {
        if ($country instanceof Country) {
            return $this
                ->addUsingAlias(CustomerPeer::COUNTRY_ID, $country->getId(), $comparison);
        } elseif ($country instanceof PropelObjectCollection) {
            if (null === $comparison) {
                $comparison = Criteria::IN;
            }

            return $this
                ->addUsingAlias(CustomerPeer::COUNTRY_ID, $country->toKeyValue('PrimaryKey', 'Id'), $comparison);
        } else {
            throw new PropelException('filterByCountry() only accepts arguments of type Country or PropelCollection');
        }
    }