PHP SimpleXML XPath contains() to find other elements referenced by this element

Question

Hi Guys ang Gals,

I'm being given XML in the following format, and am parsing it with PHP's SimpleXML.

<?xml version="1.0" encoding="UTF-8"?>
<ManageMyBooking>
    <BookingInfo>
        <PartyDetails>
            <Passenger>
                <PaxNo>1</PaxNo>
                <Title>Mrs</Title>
                <Surname>Murphy</Surname>
            </Passenger>
            <Passenger>
                <PaxNo>2</PaxNo>
                <Title>Mr</Title>
                <Surname>Murphy</Surname>
            </Passenger>
            <Passenger>
                <PaxNo>3</PaxNo>
                <Title>Miss</Title>
                <Surname>Murphy</Surname>
            </Passenger>
        </PartyDetails>
        <Accommodation>
            <Units>
                <Unit>
                    <UnitNo>1</UnitNo>
                    <UnitDesc>...</UnitDesc>
                    <PaxAssociated>1|2</PaxAssociated>
                </Unit>
                <Unit>
                    <UnitNo>2</UnitNo>
                    <UnitDesc>...</UnitDesc>
                    <PaxAssociated>3</PaxAssociated>
                </Unit>
            </Units>
        </Accommodation>
    </BookingInfo>
</ManageMyBooking>

I'm looping through the Units (Rooms) thus:

// $Accommodation is a SimpleXML Object defined earlier, and able to provide relevant info
<?  foreach ($Accommodation->Units as $Units) {
     foreach ($Units->Unit as $Unit) {
     // (room/unit details echoed out here)
      foreach ($Unit->xpath('//Passenger[contains(PaxAssociated,./PaxNo)]') as $RoomPax) { ?>
<?= $RoomPax->Title $RoomPax->Surname" ?><br />
<?= "$RoomPax->Title $RoomPax->Surname" ?><br />
<?    }
     }
    } ?>

in an attempt to show the names off the Passengers (Pax) in each room.

But this xpath finds no-one, and the following gets everyone.

//Passenger[contains(PaxNo,./PaxAssociated)]

What's especially frustrating is that I've successfully used XPath elsewhere in the same PHP for a very similar purpose, with no problems.

Any help/advice/suggestions will be much appreciated.

---

Edit: for completeness, and to answer a question from multiple people: The following works elsewhere in the code, (though not 100% correctly given the possible matching on '22' vs '2'.

//Flight[contains(PaxAssociated,./PaxNo)]

Answer 1

This:

//Passenger[contains(PaxNo,./PaxAssociated)]

is: Find any <Passenger> with a child <PaxNo> who's value contains the value of the child <PaxAssociated>. It would only work with such a data structure (which you clearly don't have):

<ManageMyBooking>
  <BookingInfo>
    <PartyDetails>
      <Passenger>
        <PaxNo>1|2</PaxNo>  <!-- note the exchanged value! -->
        <PaxAssociated>1</PaxAssociated>
      </Passenger>
    </PartyDetails>
  </BookingInfo>
</ManageMyBooking>

So this is wrong on multiple accounts. What you mean is probably a dynamic XPath expression, like this:

foreach ($Units->Unit as $Unit) {
  $XPath = "//Passenger[contains('". $Unit->PaxAssociated . "', PaxNo)]";
  foreach ($Unit->xpath($XPath) as $RoomPax) {
    // ...
  }
}

This works on first glance, but it is not fail-safe, because "22" contains "2" as well. So doing a contains() alone won't get you anywhere. Correct would be:

$XPath = "//Passenger[contains('|". $Unit->PaxAssociated ."|', concat('|', PaxNo, '|'))]";

This way you check "|22|" against "|2|", which would return false.