XPath语法
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使用路径表达式来选择XML文档的节或是节集。顺着路径或步骤来选择节。
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使用路径表达式来选择XML文档的节或是节集。顺着路径或步骤来选择节。
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## The XML Example Document
XML实例文档
We will use the following XML document in the examples below.
举例中我们将使用下面的XML文档
>
>
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## Selecting Nodes
选择节
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:
一些非常有用的路径表达式：
| **表达式** | **描述** |
| *nodename* | Selects all child nodes of the node[选择所有目前节的子节] |
| / | Selects from the root node[从根节进行选择] |
| // | Selects nodes in the document from the current node that match the selection no matter where they are [选择文档中相吻合的节而不管其在文档的何处] |
| . | Selects the current node[选择当前节] |
| .. | Selects the parent of the current node[当前节的父节] |
| @ | Selects attributes[选择属性] |
### Examples
实例
In the table below we have listed some path expressions and the result of the expressions:
下面我们所列举的表格有路径表达式以及其结果：
| **路径表达式** | **结果** |
| bookstore | Selects all the child nodes of the bookstore element[选择所有bookstore元素的子节] |
| /bookstore | Selects the root element bookstore **Note:** If the path starts with a slash ( / ) it always represents an absolute path to an element! [选择了bookstore的根元素。注意：如果路径的开始为(/)那此路径一定是到该元素的绝对路径] |
| bookstore/book | Selects all book elements that are children of bookstore[选择了所有在bookstore的子元素book元素所包含的所有元素（其实就为bookstore里book元素所包含的元素）] |
| //book | Selects all book elements no matter where they are in the document[选择所有为book元素的内容而不管book元素处于何处(有不同的父也没关系)] |
| bookstore//book | Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element[在bookstore元素内所有含有book元素的元素内容（只要book元素的祖元素为bookstore元素那都符合条件）] |
| //@lang | Selects all attributes that are named lang[选择所有属性名为lang的属性] |
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## Predicates
谓语
Predicates are used to find a specific node or a node that contains a specific value.
谓语用来指定明确的节所含有的特殊的值
Predicates are always embedded in square brackets.
谓语被嵌入在中括号
### Examples
举例
In the table below we have listed some path expressions with predicates and the result of the expressions:
下面的表格列举了一些使用了谓语的路径表达式以及其产生的结果：
| **路径表达式** | **结果** |
| /bookstore/book[1] | Selects the first book element that is the child of the bookstore element[选择了bookstore里的第一个book元素] |
| /bookstore/book[last()] | Selects the last book element that is the child of the bookstore element[选择bookstore里最后一个book元素] |
| /bookstore/book[last()-1] | Selects the last but one book element that is the child of the bookstore element[bookstore中倒数第二个book元素] |
| /bookstore/book[position()<3] | Selects the first two book elements that are children of the bookstore element[在bookstore中前两个book元素] |
| //title[@lang] | Selects all the title elements that have an attribute named lang[选择所有含有lang属性的title元素] |
| //title[@lang='eng'] | Selects all the title elements that have an attribute named lang with a value of 'eng'[选择所有含有lang属性并且值为eng的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[选择所有bookstore中book元素里price元素内容大于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 gr eater than 35.00[选择bookstore中book的子元素title，并且其兄弟元素price的内容得大于35.00] |
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## Selecting Unknown Nodes
选择未知的节
XPath wildcards can be used to select unknown XML elements.
XPath的通配符可以用来选择未知的XML元素
| **通配符** | **描述** |
| * | Matches any element node[相吻合的所有元素节] |
| @* | Matches any attribute node[相吻合的所有属性节] |
| node() | Matches any node of any kind[吻合任何类型的节] |
### Examples实例
In the table below we have listed some path expressions and the result of the expressions:
下面的表格我们将列举一些路径表达式以及它们的结果
| **路径表达式** | **结果** |
| /bookstore/* | Selects all the child nodes of the bookstore element[选择所有bookstore的子节] |
| //* | Selects all elements in the document[选择所有文档中的元素] |
| //title[@*] | Selects all title elements which have any attribute[选择元素为title并且其含有属性] |
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## Selecting Several Paths
选择数个路径
By using the | operator in an XPath expression you can select several paths.
通过在XPath中使用 | 你可以选择数个路径
### Examples
实例
In the table below we have listed some path expressions and the result of the expressions:
下面的表格我们会列举一些路径表达式以及其结果：
| **路径表达** | **结果** |
| //book/title | //book/price | Selects all the title AND price elements of all book elements[选择所有book里title和price元素] |
| //title | //price | Selects all the title AND price elements in the document[选择所有title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[选择所有book里的title元素和所有price元素] |
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