xml XPath 查找具有特定子节点的所有元素
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XPath find all elements with specific child node
提问by nam
Could you please help me to find all the elements b which have the child element c in the example below?
你能帮我在下面的例子中找到所有具有子元素 c 的元素 b 吗？
<a>
<b name = "b1"></b>
<b name = "b2"><c/></b>
<b name = "b3"></b>
</a>
The xpath query must return the b2 element
xpath 查询必须返回 b2 元素
The second question is I want to combine 2 conditions: I want to get the element which have name = "b2" and has the element c But this syntax seems not to work: //b[@name='b2' and c]
第二个问题是我想结合两个条件：我想得到 name = "b2" 并且有元素 c 的元素但是这个语法似乎不起作用：//b[@name='b2' and c]
回答by Dimitre Novatchev
Whenever the structure of the XML document is known, it is better to avoid using the //XPath pseudo-operator, as its use can result in big inefficiency (traversal of the whole document tree).
只要知道 XML 文档的结构，最好避免使用//XPath 伪运算符，因为它的使用会导致效率低下（遍历整个文档树）。
Therefore, I recomment this XPath expression for the provided XML document:
因此，我为所提供的 XML 文档推荐此 XPath 表达式：
/*/b[c]
This selects any belement that is a child of the top element of the XML document and that has a child-element named c.
这将选择b作为 XML 文档顶部元素的子元素并且具有名为 的子元素的任何元素c。
UPDATE: The OP asked a second question just minutes ago:
更新：OP 几分钟前问了第二个问题：
The second question is I want to combine 2 conditions: I want to get the element which have name = "b2" and has the element c But this syntax seems not to work:
//b[@name='b2' and c]
第二个问题是我想结合两个条件：我想获得 name = "b2" 并且有元素 c 的元素但是这个语法似乎不起作用：
//b[@name='b2' and c]
The provided XPath expression doesselect exactly the wanted element.
提供的 XPath 表达式确实选择了所需的元素。
Here is XSLT - based verification:
这是基于 XSLT 的验证：
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:template match="/*">
<xsl:copy-of select="//b[@name='b2' and c]"/>
</xsl:template>
</xsl:stylesheet>
When this transformation is applied on the provided XML document:
当此转换应用于提供的 XML 文档时：
<a>
<b name = "b1"></b>
<b name = "b2"><c/></b>
<b name = "b3"></b>
</a>
the XPath expression is evaluated and the correctly-selected element is copied to the output:
计算 XPath 表达式并将正确选择的元素复制到输出：
<b name="b2">
<c/>
</b>
回答by choroba
It should be as simple as
应该很简单
//b[c]
i.e. find a banywhere that has a cchild.
即找到一个b有c孩子的地方。
