php xpath与dom如何编写更短的查询

Question

The xml file that I need to get out data is large and has lot of inner children in children. The XML on what I need to query looks like in the picture and it has more Ref children in company. xml structure

I need to get the company node that has the correct Info->ID. That node has 3 Ref nodes and I need to get Date from the one that has the correct Who.

I got this working with this ugly code:

$query_pod = "//Seller/Company/Info/ID[ID = 'IV'] | //Seller/Company/Ref/Who[Who = 'VA'] | //Seller/Company/Ref/Date";
foreach ($xpath->query( $query_pod ) as $pod)
{
    $pod_dates = $xpath->query( "//Seller/Company/Ref/Who[Who = 'VA'] | //Seller/Company/Ref/Date", $pod );
    $pod_date = $pod_dates->item(0)->nodeValue;
}

I tryed it shorter but I cant get the select element in [] like this:

$query_pod = "//Seller/Company/Info[ID = 'IV']";
foreach ($xpath->query( $query_pod ) as $pod)
{
    $pod_dates = $xpath->query( "//Seller/Company/Ref/Date[Who = 'VA'], $pod );
    $pod_date = $pod_dates->item(0)->nodeValue;
}

Can someone help? I'm new to xpath.

Answer 1

You second expression (the on inside the loop) does not depend on the context. A slash (/) at the begin of a location path means that is absolute, it starts at the document node. [] are conditions that filter the result from the previous location path. They are full Xpath expression themselves. So no, it is not always possible to shorten the Xpath expressions. But in you case you can fetch the company node as a list and then the details directly using DOMXpath::evaluate(). Unlike DOMXpath::query(), DOMXpath::evaluate() can return node lists or scalar values. It depending on the expression.

$xml = <<<'XML'
<Seller>
  <Company>
    <Info> 
      <ID>123</ID>
      <Address>Some street, somewhere</Address>
    </Info>
    <Ref>
      <Who>456</Who>
      <Date>2017-01-05T01:59Z</Date>
    </Ref>
  </Company>
</Seller>
XML;

$document = new DOMDocument();
$document->loadXml($xml);
$xpath = new DOMXpath($document);

foreach ($xpath->evaluate('/Seller/Company[Info/ID = "123"]') as $company) {
  var_dump(
    $xpath->evaluate('string(Info/ID)', $company),
    $xpath->evaluate('string(Ref/Date)', $company)
  );
}

Output:

string(3) "123"
string(17) "2017-01-05T01:59Z"

If you only need a single value you can fetch it directly:

var_dump(
  $xpath->evaluate('string(/Seller/Company[Info/ID = "123"]/Ref/Date)')
);