Path Axes

最新推荐文章于 2025-12-04 19:14:36 发布

转载最新推荐文章于 2025-12-04 19:14:36 发布 · 306 阅读

文章标签：

#path #attributes #encoding #each #xml

本文详细介绍了 XPath 中的各种轴，如祖先轴、属性轴等，并通过实例展示了如何使用这些轴来定位 XML 文档中的节点。此外，还解释了绝对与相对位置路径的概念及其在 XPath 表达式中的应用。

Path Axes

The XML Example Document

We will use the following XML document in the examples below.

<?xml version="1.0" encoding="ISO-8859-1"?>

<bookstore>

<book>
  <title lang="eng">Harry Potter</title>
  <price>29.99</price>
</book>

<book>
  <title lang="eng">Learning XML</title>
  <price>39.95</price>
</book>

</bookstore>

XPath Axes

An axis defines a node-set relative to the current node.

AxisName	Result
ancestor	Selects all ancestors (parent, grandparent, etc.) of the current node
ancestor-or-self	Selects all ancestors (parent, grandparent, etc.) of the current node and the current node itself
attribute	Selects all attributes of the current node
child	Selects all children of the current node
descendant	Selects all descendants (children, grandchildren, etc.) of the current node
descendant-or-self	Selects all descendants (children, grandchildren, etc.) of the current node and the current node itself
following	Selects everything in the document after the closing tag of the current node
following-sibling	Selects all siblings after the current node
namespace	Selects all namespace nodes of the current node
parent	Selects the parent of the current node
preceding	Selects everything in the document that is before the start tag of the current node
preceding-sibling	Selects all siblings before the current node
self	Selects the current node

Location Path Expression

A location path can be absolute or relative.

An absolute location path starts with a slash ( / ) and a relative location path does not. In both cases the location path consists of one or more steps, each separated by a slash:

An absolute location path:

/step/step/...

A relative location path:

step/step/...

Each step is evaluated against the nodes in the current node-set.

A step consists of:

an axis (defines the tree-relationship between the selected nodes and the current node)
a node-test (identifies a node within an axis)
zero or more predicates (to further refine the selected node-set)

The syntax for a location step is:

axisname::nodetest[predicate]

Examples

Example	Result
child::book	Selects all book nodes that are children of the current node
attribute::lang	Selects the lang attribute of the current node
child::*	Selects all children of the current node
attribute::*	Selects all attributes of the current node
child::text()	Selects all text child nodes of the current node
child::node()	Selects all child nodes of the current node
descendant::book	Selects all book descendants of the current node
ancestor::book	Selects all book ancestors of the current node
ancestor-or-self::book	Selects all book ancestors of the current node - and the current as well if it is a book node
child::*/child::price	Selects all price grandchildren of the current node