xPath -当节点缺席时返回默认值？

Question

我看到了多个堆叠溢出的帖子来寻找答案，但却找不到。尝试了这么多的可能性，但似乎没有什么效果。

我想找到gsRating的学校下面，但很多它的可选标签。因此，希望在缺席时将-1作为默认值返回。

以下是XML：

<?xml version="1.0" encoding="UTF-8"?>
<schools>
   <school>
      <gsId>87</gsId>
      <name>James Leitch Elementary School</name>
      <type>public</type>
      <gradeRange>K-3</gradeRange>
      <enrollment>1075</enrollment>
      <gsRating>10</gsRating>
      <parentRating>4</parentRating>
      <city>Fremont</city>
      <state>CA</state>
      <districtId>8</districtId>
      <district>Fremont Unified</district>
      <districtNCESId>0614400</districtNCESId>
      <address>47100 Fernald Street, 
Fremont, CA  94539</address>
      <phone>(510) 657-6100</phone>
      <fax>(510) 659-9298</fax>
      <website>http://www.jleitch.edu/</website>
      <ncesId>061440001673</ncesId>
      <lat>37.486492</lat>
      <lon>-121.92332</lon>
      <overviewLink>http://www.greatschools.org/california/fremont/87-James-Leitch-Elementary-School/?s_cid=gsapi</overviewLink>
      <ratingsLink>http://www.greatschools.org/school/rating.page?state=CA&amp;id=87&amp;s_cid=gsapi</ratingsLink>
      <reviewsLink>http://www.greatschools.org/school/parentReviews.page?state=CA&amp;id=87&amp;s_cid=gsapi</reviewsLink>
      <distance>1.12</distance>
      <schoolStatsLink>http://www.greatschools.org/modperl/achievement/CA/87</schoolStatsLink>
   </school>
   <school>
      <gsId>107</gsId>
      <name>Fred E. Weibel Elementary School</name>
      <type>public</type>
      <gradeRange>K-6</gradeRange>
      <enrollment>853</enrollment>
      <parentRating>4</parentRating>
      <city>Fremont</city>
      <state>CA</state>
      <districtId>8</districtId>
      <district>Fremont Unified</district>
      <districtNCESId>0614400</districtNCESId>
      <address>45135 South Grimmer Boulevard, 
Fremont, CA  94539</address>
      <phone>(510) 651-6958</phone>
      <fax>(510) 651-6653</fax>
      <website>http://www.fremont.k12.ca.us/weibel/</website>
      <ncesId>061440009139</ncesId>
      <lat>37.507336</lat>
      <lon>-121.92837</lon>
      <overviewLink>http://www.greatschools.org/california/fremont/107-Fred-E.-Weibel-Elementary-School/?s_cid=gsapi</overviewLink>
      <ratingsLink>http://www.greatschools.org/school/rating.page?state=CA&amp;id=107&amp;s_cid=gsapi</ratingsLink>
      <reviewsLink>http://www.greatschools.org/school/parentReviews.page?state=CA&amp;id=107&amp;s_cid=gsapi</reviewsLink>
      <distance>1.14</distance>
      <schoolStatsLink>http://www.greatschools.org/modperl/achievement/CA/107</schoolStatsLink>
   </school>
</schools>

尝试如下：

//schools/school[*]/(gsRating/string(),'-1')[1]

Answer 1

试作如下： //学校/学校*/(gsRating/string()，'-1')1

使用此XPath 2.0表达式

/*/*/(string(gsRating)[.], -1)[1]

如果要丢弃字符串值为空格的gsRatings 元素，请使用：

/*/*/(normalize-space(gsRating)[.], -1)[1]

如果要丢弃任何字符串值不能转换为数字gsRatings 的，请使用：

/*/*/(normalize-space(gsRating)[number(.) eq number(.)], -1)[1]

这里是一个基于XSLT的验证。

为了简单起见，让我们使用以下XML文档：

<schools>
    <school>
        <gsRating>10</gsRating>
    </school>
    <school>
        <noRating>10</noRating>
    </school>
    <school>
        <gsRating> t </gsRating> 
    </school>
    <school>
        <gsRating/>
    </school>
    <school>
        <gsRating>  </gsRating>
    </school>
</schools>

时，此XSLT转换

<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output method="text"/>

  <xsl:template match="/*">
    <xsl:value-of select=
          "/*/*/(normalize-space(gsRating)[number(.) eq number(.)], -1)[1]"/>
  </xsl:template>
</xsl:stylesheet>

应用于上面的XML文档，计算XPath表达式并输出它产生的结果(整数序列)：

10 -1 -1 -1 -1

Answer 2

这个XPath 2.0表达式，

for $s in //school 
   return concat($s/name, ', ', if ($s/gsRating) then $s/gsRating else '-1')

会回来

James Leitch Elementary School, 10
Fred E. Weibel Elementary School, -1

对于您的示例XML。