来自 DOM 对象的 getAttribute 不返回属性

Question

我正在编写一个程序，该程序从多个外部来源获取经济和社会统计数据，并将它们提取到数据库中（用于数据分析）。一些数据采用 XML 格式，为了解析它，我需要识别 XML 文件中的元素/标签以及属性。为了识别我尝试使用 getAttribute 的属性。

问题：虽然 getElementsByTagName 有效，但 getAttribute 无效。尝试从单元格元素中检索属性“索引”的值会返回“”，即使属性“索引”确实存在于许多单元格元素中。没有错误，只是没有返回值。

我花了几天时间阅读 PHP 手册并研究 Internet 以尝试找到解决方案，但没有成功。 getAttribute 的返回值上的回显或 var_dump 表明它始终返回“”。 我没有放整个源代码，而是复制了一个读取下面 XML 文件的更简单版本，它会遇到同样的问题，即无法返回属性（在本例中为“索引”属性）。

<?php

// Creates new DOMDocument
$dom = new DOMDocument();
// Loads XML file into DOMDocument
$dom->load('FRED_formatted_list.xml');

// Stores all the instances of the Row tag into $rows
$rows = $dom->getElementsByTagName('Row');

// Iterates through all the instances of the Row tag
foreach($rows as $row) {

// Stores all the instances of the Cell tag into $cells
$cells = $row->getElementsByTagName('Cell');

// Iterates through all the instances of the Cell tag
foreach($cells as $cell) {

    // Checks if the Index attribute exists in the cell tag
    if($cell->hasAttribute('Index')) {
        // Stores the value of any instances of the Index attribute
        $attr = $cell->getAttribute('Index');
        // Prints the value of any instances of the Index attribute to screen
        echo "Value of index attribute: " . $attr . "<br>";

    }
    // Check that the cell tags have been properly identified in the DOM Object
    echo $cell->nodeValue . "<br>";
    // Double checks whether any index values are even found and stored in $attr
    var_dump($attr) . "<br>";
}
}
?>

这是一个 XML 文件的示例，它显示属性“索引”确实存在，即使 getAttributes 没有返回：

<Row>
    <Cell><Data ss:Type="String">AAA</Data></Cell>
    <Cell ss:Index="3"><Data ss:Type="String">Board of Governors of the Federal Reserve System (US)</Data></Cell>
    <Cell><Data ss:Type="String">H.15 Selected Interest Rates</Data></Cell>
    <Cell><Data ss:Type="String">Percent</Data></Cell>
    <Cell><Data ss:Type="String">Not Seasonally Adjusted</Data></Cell>
    <Cell><Data ss:Type="String">The Federal Reserve Board has discontinued this series as of October 11, 2016. More information, including possible alternative series, can be found at http://www.federalreserve.gov/feeds/h15.html. </Data></Cell>
</Row>

任何帮助将不胜感激。我将总结解决方案并重新发布以帮助他人。

Answer 1

经过进一步研究，我发现其他人遇到了这个问题并设法解决了它。 XML 单元标记/元素中的属性“索引”以“ss:”为前缀（根据上面的 XML 文件提取 <Cell ss:Index="3"><Data ss:Type="String">）。要使 getAttribute 起作用，需要包含“ss：”，例如正确的代码是 getAttribute('ss:Index') 而不是 getAttribute('Index')
我不完全理解getAttribute 是如何识别一个属性的，但它可能是搜索一个前面带有空格的连续字符的字符串，因此需要包含'ss:'。

Answer 2

在 xml 中定义命名空间：

<Row xmlns:ss="something">
  <Cell><Data ss:Type="String">AAA</Data></Cell>
  <Cell ss:Index="3"><Data ss:Type="String">Board of Governors of the Federal Reserve System (US)</Data></Cell>
  <Cell><Data ss:Type="String">H.15 Selected Interest Rates</Data></Cell>
  <Cell><Data ss:Type="String">Percent</Data></Cell>
  <Cell><Data ss:Type="String">Not Seasonally Adjusted</Data></Cell>
  <Cell><Data ss:Type="String">The Federal Reserve Board has discontinued this series as of October 11, 2016. More information, including possible alternative series, can be found at http://www.federalreserve.gov/feeds/h15.html. </Data></Cell>
</Row>

尝试使用以下代码获取具有命名空间的属性值：

<?php

  // Creates new DOMDocument
  $dom = new DOMDocument();
  // Loads XML file into DOMDocument
  $dom->load('FRED_formatted_list.xml');

  // Stores all the instances of the Row tag into $rows
  $rows = $dom->getElementsByTagName('Row');
  $attr ='';
  // Iterates through all the instances of the Row tag
  foreach($rows as $row) {

     // Stores all the instances of the Cell tag into $cells
     $cells = $row->getElementsByTagName('Cell');

    // Iterates through all the instances of the Cell tag
    foreach($cells as $cell) {
        // Checks if the Index attribute exists in the cell tag
       if($cell->attributes->getNamedItem('Index')) {
           // Stores the value of any instances of the Index attribute
           $attr = $cell->attributes->getNamedItem('Index')->nodeValue;
           // Prints the value of any instances of the Index attribute to screen
            echo "Value of index attribute: " . $attr . "<br>";

        }
     // Check that the cell tags have been properly identified in the DOM Object
     echo $cell->nodeValue . "<br>";
     // Double checks whether any index values are even found and stored in $attr
     var_dump($attr) . "<br>";


   }

}