Foreach on an array of objects not working PHP

Question

So I have XML in $xml. It looks like this:

http://localhost:8888/?purp=oclcn&xml=<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<record xmlns="http://www.loc.gov/MARC21/slim">
    <leader>00000cam a2200000 a 4500</leader>
    <controlfield tag="001">33333502</controlfield>
    <controlfield tag="008">951010s1996    vtua     b    001 0 eng  </controlfield>
    <datafield ind1=" " ind2=" " tag="010">
      <subfield code="a">   95045582 </subfield>
    </datafield>
    <datafield ind1=" " ind2=" " tag="020">
      <subfield code="a">1858983274</subfield>
    </datafield>
    <datafield ind1=" " ind2=" " tag="020">
      <subfield code="a">9781858983271</subfield>
    </datafield>
    <datafield ind1="0" ind2="0" tag="245">
      <subfield code="a">Economic sociology /</subfield>
      <subfield code="c">edited by Richard Swedberg.</subfield>
    </datafield>
    <datafield ind1=" " ind2=" " tag="260">
      <subfield code="a">Cheltenham, Glos, UK ;</subfield>
      <subfield code="a">Brookfield, Vt., US :</subfield>
      <subfield code="b">E. Elgar Pub. Co.,</subfield>
      <subfield code="c">©1996.</subfield>
    </datafield>
    <datafield ind1=" " ind2=" " tag="300">
      <subfield code="a">xv, 574 pages :</subfield>
      <subfield code="b">illustrations ;</subfield>
      <subfield code="c">25 cm.</subfield>
    </datafield>
    <datafield ind1="1" ind2=" " tag="490">
      <subfield code="a">The international library of critical writings in sociology ;</subfield>
      <subfield code="v">5</subfield>
    </datafield>
    <datafield ind1="1" ind2=" " tag="490">
      <subfield code="a">An Elgar reference collection</subfield>
    </datafield>
    <datafield ind1=" " ind2=" " tag="500">
      <subfield code="a">A collection of journal articles previously published between 1940-1994.</subfield>
    </datafield>
    <datafield ind1=" " ind2="0" tag="650">
      <subfield code="a">Economics</subfield>
      <subfield code="x">Sociological aspects.</subfield>
    </datafield>
    <datafield ind1=" " ind2="0" tag="650">
      <subfield code="a">Sociology.</subfield>
    </datafield>
    <datafield ind1=" " ind2="0" tag="650">
      <subfield code="a">Economics.</subfield>
    </datafield>
    <datafield ind1=" " ind2="6" tag="650">
      <subfield code="a">Économie politique</subfield>
      <subfield code="x">Aspect sociologique.</subfield>
    </datafield>
    <datafield ind1=" " ind2="6" tag="650">
      <subfield code="a">Sociologie.</subfield>
    </datafield>
    <datafield ind1=" " ind2="6" tag="650">
      <subfield code="a">Économie politique.</subfield>
    </datafield>
    <datafield ind1=" " ind2="7" tag="650">
      <subfield code="a">Economics.</subfield>
      <subfield code="2">fast</subfield>
      <subfield code="0">(OCoLC)fst00902116</subfield>
    </datafield>
    <datafield ind1=" " ind2="7" tag="650">
      <subfield code="a">Economics</subfield>
      <subfield code="x">Sociological aspects.</subfield>
      <subfield code="2">fast</subfield>
      <subfield code="0">(OCoLC)fst00902213</subfield>
    </datafield>
    <datafield ind1=" " ind2="7" tag="650">
      <subfield code="a">Sociology.</subfield>
      <subfield code="2">fast</subfield>
      <subfield code="0">(OCoLC)fst01123875</subfield>
    </datafield>
    <datafield ind1="1" ind2="7" tag="650">
      <subfield code="a">Economische sociologie.</subfield>
      <subfield code="2">gtt</subfield>
    </datafield>
    <datafield ind1=" " ind2="7" tag="650">
      <subfield code="a">Sociologie économique.</subfield>
      <subfield code="2">ram</subfield>
    </datafield>
    <datafield ind1=" " ind2="7" tag="650">
      <subfield code="a">Économie politique</subfield>
      <subfield code="x">Sociologie.</subfield>
      <subfield code="2">ram</subfield>
    </datafield>
    <datafield ind1="0" ind2="7" tag="650">
      <subfield code="a">Wirtschaftssoziologie.</subfield>
      <subfield code="2">swd</subfield>
    </datafield>
    <datafield ind1=" " ind2="4" tag="650">
      <subfield code="a">Sociologie.</subfield>
    </datafield>
    <datafield ind1=" " ind2="4" tag="650">
      <subfield code="a">Économie politique.</subfield>
    </datafield>
    <datafield ind1=" " ind2="4" tag="650">
      <subfield code="a">Économie politique - Aspect sociologique.</subfield>
    </datafield>
    <datafield ind1="0" ind2="7" tag="650">
      <subfield code="a">Wirtschaftssoziologie.</subfield>
      <subfield code="0">(DE-588)4066514-8</subfield>
      <subfield code="2">gnd</subfield>
    </datafield>
    <datafield ind1="1" ind2=" " tag="700">
      <subfield code="a">Swedberg, Richard.</subfield>
    </datafield>
  </record>

I am trying to get the value of "tag" attribute of every element. However, the foreach loop is not working. It only echoes 008hello, and no more. How come?

$dataf = $xml->getElementsByTagName("datafield");
$controlf = $xml->getElementsByTagName("controlfield");


        $count = $dataf->length + $controlf->length;

I put the contents of each DOMNodeList into an array so I can merge them together: $DOMarray = array();

        $i = 1;
        while ($i <= $controlf->length) {
        $p = $controlf->item($i);
        $DOMarray[] = $p;
        $i++;
}

        $i = 1;
        while ($i <= $dataf->length) {
        $p = $dataf->item($i);
        $DOMarray[] = $p;
        $i++;
}

Now I wish to get the value of attribute tag of each element:

echo get_class($DOMarray[$number]);
echo sizeof($DOMarray);
foreach($DOMarray as $DOMe) {
    echo $DOMe->getAttribute("tag");
    echo "hello";
}
// echo $DOMarray[$number]->getAttribute("tag");
}
}

Please format your question. It is unreadable.

u_mulder
– u_mulder

2017-01-07 09:44:24 +00:00
Commented Jan 7, 2017 at 9:44 — u_mulder
– u_mulder, Commented Jan 7, 2017 at 9:44

BizzyBob · Accepted Answer · 2017-01-07 10:25:59Z

The problem is in the set up of your loops.

In your data, there are 2 elements in the $controlf array, however, since you are starting your counter at 1 you are skipping the first. This is why you are getting 008 and not the first value 001.

$i = 1;
    while ($i <= $controlf->length) {
    $p = $controlf->item($i);
    $DOMarray[] = $p;
    $i++;
}

To fix this, start your counter at 0 and use < rather than <=:

$i = 0;
    while ($i < $controlf->length) {
    $p = $controlf->item($i);
    $DOMarray[] = $p;
    $i++;
}

In general, when working with loops, you would usually use < because the indices of arrays are zero-based and the length property is the actual number of elements. So the length property will always be 1 higher than than the highest index value.

Also, you may find using foreach a little cleaner in this case. The following is equivalent to the code above:

foreach ($controlf as $p){
    $DOMarray[] = $p;
}

ThW · Accepted Answer · 2017-01-08 09:29:53Z

Your XML uses a namespace, so you should use the namespace aware methods, too. That means getElementsByTagNameNS(). I suggest defining the namespaces in an associative array. Here is no need to convert the DOMNodeList objects into an array using a loop. DOMNodeList implements iterator and here is a function iterator_to_array() for exactly that job. But why create the array of nodes at all, you can just iterate over the DOMNodeList and read the tag attribute.

$xmlns = [
  'slim' => 'http://www.loc.gov/MARC21/slim'
];
$document = new DOMDocument();
$document->loadXml($xml);

$result = [];
$nodes = $document->getElementsByTagNameNS($xmlns['slim'], 'controlfield');
foreach ($nodes as $node) {
  $result[] = $node->getAttribute('tag');
}
$nodes = $document->getElementsByTagNameNS($xmlns['slim'], 'datafield');
foreach ($nodes as $node) {
  $result[] = $node->getAttribute('tag');
}

var_dump($result);

Output:

array(29) {
  [0]=>
  string(3) "001"
  [1]=>
  string(3) "008"
  [2]=>
  string(3) "010"
  [3]=>
  string(3) "020"
  ...

An even easier way is to use Xpath. Attributes are nodes and Xpath allows you to fetch them directly.

$document = new DOMDocument();
$document->loadXml($xml);
$xpath = new DOMXpath($document);
$xpath->registerNamespace('slim', 'http://www.loc.gov/MARC21/slim');

$result = [];
$expression = '/slim:record/slim:controlfield/@tag|/slim:record/slim:datafield/@tag';
foreach ($xpath->evaluate($expression) as $attribute) {
  $result[] = $attribute->value;
}

var_dump($result);

Xpath 1.0 does not have a concept of a default namespace, so you need to register a prefix for it. After that you can filter the nodes in the DOM with a location path. /slim:record/slim:controlfield fetches all controlfield elements. @tag fetches the tag attribute nodes. The | acts as an OR for the filter expression.

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