XPath 簡單文法

XPath uses path expressions to select nodes or node-sets in an XML document. The node is selected by following a path or steps.
XPath 通過路徑運算式從XML文檔中選取節點或節點集。該節點是通過其後的一條語句或相應的步驟選取的。

The XML Example Document
XML 案例文檔
We will use the following XML document in the examples below.
我們將在接下來的案例中引用下面這個XML文檔：

<?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>

Selecting Nodes
選取節點
XPath uses path expressions to select nodes in an XML document. The node is selected by following a path or steps. The most useful path expressions are listed below:
XPath使用路徑運算式在XML文檔中選取節點。該節點是通過其後的一條語句或相應的步驟選取的。下面列出了最常用的路徑運算式：

Expression 運算式	Description 注釋
nodename	Selects all child nodes of the node 選取某節點中的所有子節點
/	Selects from the root node 從根節點處選取
//	Selects nodes in the document from the current node that match the selection no matter where they are 選取文檔中所有匹配的節點，不管該節點位於何處
.	Selects the current node 選取當前節點
..	Selects the parent of the current node 選取當前節點的父節點
@	Selects attributes 選取屬性

 

Examples
案例
In the table below we have listed some path expressions and the result of the expressions:
在下述表格中，我們羅列了一些路徑運算式及其啟動並執行結果：

Path Expression 運算式	Result 結果
bookstore	Selects all the child nodes of the bookstore element 選取bookstore元素的所有子節點
/bookstore	Selects the root element bookstore 選取以bookstore元素為根目錄的點 Note: If the path starts with a slash ( / ) it always represents an absolute path to an element! 注意：如果一個路徑以（/）開始，那麼它代表該元素的絕對路徑！
bookstore/book	Selects all book elements that are children of bookstore 選取bookstore中的所有book子項目
//book	Selects all book elements no matter where they are in the document 選取文檔中的所有book元素
bookstore//book	Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element 選取文檔中所有處於bookstore節點下的book元素
//@lang	Selects all attributes that are named lang 選取所有指定的lang屬性

Predicates
條件
Predicates are used to find a specific node or a node that contains a specific value.
它指定了選取節點的範圍。
Predicates are always embedded in square brackets.
通常使用方括弧[ ]來指定條件。
Examples
執行個體
In the table below we have listed some path expressions with predicates and the result of the expressions:
在下述表格中，我們列舉了一些路徑運算式及其運行結果：

Path Expression 運算式	Result 結果
/bookstore/book[1]	Selects the first book element that is the child of the bookstore element 選取bookstore元素下的第一個book元素
/bookstore/book[last()]	Selects the last book element that is the child of the bookstore element 選取bookstore元素下的最後一個book元素
/bookstore/book[last()-1]	Selects the last but one book element that is the child of the bookstore element 選取bookstore元素下的倒數第二個book元素
/bookstore/book[position()<3]	Selects the first two book elements that are children of the bookstore element 選取bookstore元素下的前兩個book子項目
//title[@lang]	Selects all the title elements that have an attribute named lang 選取所含指定的lang屬性的有包title元素
//title[@lang='eng']	Selects all the title elements that have an attribute named lang with a value of 'eng' 選取所有lang屬性值為“eng”的所有“title”元素
/bookstore/book[price>35.00]	Selects all the book elements of the bookstore element that have a price element with a value greater than 35.00 選取bookstore元素下所有price元素值大於35.00的book元素
/bookstore/book[price>35.00]/title	Selects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 35.00 選取bookstore元素下所有price元素值大於35.00的book節點下的title元素

Selecting Unknown Nodes
選取未知節點
XPath wildcards can be used to select unknown XML elements.
可以通過 XPath 萬用字元選取未知的XML元素。

Wildcard 萬用字元	Description 說明
*	Matches any element node 匹配任意的元素節點
@*	Matches any attribute node 匹配任意的屬性節點
node()	Matches any node of any kind 匹配所有類型的節點

Examples
案例
In the table below we have listed some path expressions and the result of the expressions:
在下述表格中，我們列出了一些路徑運算式及其運行結果：

Path Expression 運算式	Result 結果
/bookstore/*	Selects all the child nodes of the bookstore element 選取bookstore元素中的所有子節點
//*	Selects all elements in the document 選取文檔中的所有元素
//title[@*]	Selects all title elements which have any attribute 選取包含任意屬性的所有title元素

Selecting Several Paths
選取多個路徑
By using the | operator in an XPath expression you can select several paths.
你可以同過在運算式中添加“ | ”操作符來選取多個路徑。
Examples
案例
In the table below we have listed some path expressions and the result of the expressions:
在下述表格中，我們列舉了一些路徑運算式及其運行結果：

Path Expression 運算式	Result 結果
//book/title | //book/price	Selects all the title AND price elements of all book elements 選取book元素中的所有title和price元素
//title | //price	Selects all the title AND price elements in the document 選取文檔中的所有title元素和price元素
/bookstore/book/title | //price	Selects all the title elements of the book element of the bookstore element AND all the price elements in the document 選取bookstore元素中book元素所對應的所有title元素以及文檔中所有的price元素