node
In XPath, there are seven types of nodes:
- element
- Attributes
- text
- Namespaces
- Processing instructions
- Comment
- Document (root) node
XML documents are treated as a tree of nodes, and the root of the tree is called the document node or root node.
-
<bookstore>(Document node) -
<author>J K. Rowling</author>(Element node) -
lang="en"(Attribute node)
Two concepts:
-
The basic value (or atomic value, Atomic value) has
no parent or no child node.J K. Rowling "en" -
Item
items are basic values or nodes
grammar
Select node
XPath uses path expressions to select nodes in an XML document. Nodes are selected by following a path or step. The most useful path expressions are listed below:
| expression | description |
|---|---|
nodename |
Select all child nodes of this node. |
/ |
Pick from the root node. |
// |
Select nodes in the document from the current node of the matching selection, regardless of their location. |
. |
Select the current node. |
.. |
Select the parent node of the current node. |
@ |
Select attributes. |
In the table below, we have listed some path expressions and their results:
| Path expression | result |
|---|---|
| bookstore | Select all child nodes of the bookstore element. |
| /bookstore | Select the root element bookstore. Note: If the path starts with a forward slash (/ ), this path always represents the absolute path to an element! |
| bookstore/book | Select all book elements that are child elements of bookstore. |
| //book | Select all book sub-elements, regardless of their position in the document. |
| bookstore//book | Select all book elements that are descendants of the bookstore element, regardless of where they are located under the bookstore. |
| // @ lang | Select all attributes named lang. |
Predicates
The predicate is used to find a specific node or a node containing a specified value.
The predicate is embedded in square brackets.
In the following table, we list some path expressions with predicates and the results of the expressions:
| Path expression | result |
|---|---|
| /bookstore/book[1] | Select the first book element that belongs to the bookstore child element. |
| /bookstore/book[last()] | Select the last book element that belongs to the bookstore child element. |
| /bookstore/book[last()-1] | Select the penultimate book element that belongs to the bookstore child element. |
| /bookstore/book[position() < 3] | Select the first two book elements that are child elements of the bookstore element. |
| // title [@lang] | Select all title elements that have an attribute named lang. |
| // title [@ lang = 'eng'] | Select all title elements, and these elements have a lang attribute with a value of eng. |
| /bookstore/book[price>35.00] | Select all book elements of the bookstore element, and the value of the price element must be greater than 35.00. |
| /bookstore/book[price>35.00]//title | Select all the title elements of the book element in the bookstore element, and the value of the price element must be greater than 35.00. |
Select unknown node
XPath wildcards can be used to select unknown XML elements.
| Wildcard | description |
|---|---|
| * | Match any element node. |
| @* | Match any attribute node. |
| node() | Match any type of node. |
In the following table, we list some path expressions and the results of these expressions:
| Path expression | result |
|---|---|
| /bookstore/* | Select all child elements of the bookstore element |
| //* | Select all elements in the document. |
| //title[@*] | Select all title elements with attributes. |
Select several paths
By using the "|" operator in the path expression, you can select several paths.
In the following table, we list some path expressions and the results of these expressions:
| Path expression | result |
|---|---|
//book/title | //book/price |
Select all the title and price elements of the book element. |
//title | //price |
Select all the title and price elements in the document. |
/bookstore/book/title | //price |
Select all the title elements of the book element belonging to the bookstore element and all the price elements in the document. |
Axes
The axis can define a node set relative to the current node.
| Axis name | result |
|---|---|
| ancestor | Select all ancestors (parents, grandfathers, etc.) of the current node. |
| ancestor-or-self | Select all ancestors (parents, grandfathers, etc.) of the current node and the current node itself. |
| attribute | 选取当前节点的所有属性。 |
| child | 选取当前节点的所有子元素。 |
| descendant | 选取当前节点的所有后代元素（子、孙等）。 |
| descendant-or-self | 选取当前节点的所有后代元素（子、孙等）以及当前节点本身。 |
| following | 选取文档中当前节点的结束标签之后的所有节点。 |
| following-sibling | 选取当前节点之后的所有兄弟节点 |
| namespace | 选取当前节点的所有命名空间节点。 |
| parent | 选取当前节点的父节点。 |
| preceding | 选取文档中当前节点的开始标签之前的所有节点。 |
| preceding-sibling | 选取当前节点之前的所有同级节点。 |
| self | 选取当前节点。 |
运算符
XPath 表达式可返回节点集、字符串、逻辑值以及数字。
| 运算符 | 描述 | 实例 | 返回值 |
|---|---|---|---|
| |
计算两个节点集 | //book | //cd |
返回所有拥有 book 和 cd 元素的节点集 |
| + | 加法 | 6 + 4 | 10 |
| - | 减法 | 6 - 4 | 2 |
| * | 乘法 | 6 * 4 | 24 |
| div | 除法 | 8 div 4 | 2 |
| = | 等于 | price=9.80 | 如果 price 是 9.80，则返回 true。 如果 price 是 9.90，则返回 false。 |
| != | 不等于 | price!=9.80 | 如果 price 是 9.90，则返回 true。 如果 price 是 9.80，则返回 false。 |
| < | 小于 | price<9.80 | 如果 price 是 9.00，则返回 true。 如果 price 是 9.90，则返回 false。 |
| <= | 小于或等于 | price<=9.80 | 如果 price 是 9.00，则返回 true。如果 price 是 9.90，则返回 false。 |
| > | 大于 | price>9.80 | 如果 price 是 9.90，则返回 true。 如果 price 是 9.80，则返回 false。 |
| >= | 大于或等于 | price>=9.80 | 如果 price 是 9.90，则返回 true。 如果 price 是 9.70，则返回 false。 |
| or | 或 | price=9.80 or price=9.70 | 如果 price 是 9.80，则返回 true。 如果 price 是 9.50，则返回 false。 |
| and | versus | price>9.00 and price<9.90 | If price is 9.80, return true. If price is 8.50, false is returned. |
| mod | Calculate the remainder of division | 5 mod 2 | 1 |