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XPath Axes


The XML Example Document

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

<?xml version="1.0" encoding="UTF-8"?>

<bookstore>

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

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

</bookstore>

XPath轴

An axis represents a relationship to the context (current) node, and is used to locate nodes relative to that node on the tree.

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 all nodes that appear before the current node in the document, except ancestors, attribute nodes and namespace nodes
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]

示例

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 element children of the current node
attribute::* Selects all attributes of the current node
child::text() Selects all text node children of the current node
child::node() Selects all children 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




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