Sintaxis XPath
XPath usa expresiones de ruta para seleccionar nodos o conjuntos de nodos en un documento XML. El nodo se selecciona siguiendo un camino o pasos.
El documento de ejemplo XML
Usaremos el siguiente documento XML en los ejemplos a continuación.
<?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>
Selección de nodos
XPath usa expresiones de ruta para seleccionar nodos en un documento XML. El nodo se selecciona siguiendo un camino o pasos. Las expresiones de ruta más útiles se enumeran a continuación:
| Expression | Description |
|---|---|
| nodename | Selects all nodes with the name "nodename" |
| / | Selects from the root node |
| // | Selects nodes in the document from the current node that match the selection no matter where they are |
| . | Selects the current node |
| .. | Selects the parent of the current node |
| @ | Selects attributes |
En la siguiente tabla, hemos enumerado algunas expresiones de ruta y el resultado de las expresiones:
| Path Expression | Result |
|---|---|
| bookstore | Selects all nodes with the name "bookstore" |
| /bookstore | Selects the root element bookstore Note: If the path starts with a slash ( / ) it always represents an absolute path to an element! |
| bookstore/book | Selects all book elements that are children of bookstore |
| //book | Selects all book elements no matter where they are in the document |
| bookstore//book | Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element |
| //@lang | Selects all attributes that are named lang |
predicados
Los predicados se utilizan para encontrar un nodo específico o un nodo que contiene un valor específico.
Los predicados siempre están incrustados entre corchetes.
En la siguiente tabla, hemos enumerado algunas expresiones de ruta con predicados y el resultado de las expresiones:
| Path Expression | Result |
|---|---|
| /bookstore/book[1] | Selects the first book element that is the child of the bookstore element.
Note: In IE 5,6,7,8,9 first node is[0], but according to W3C, it is [1]. To solve this problem in IE, set the SelectionLanguage to XPath: In JavaScript: xml.setProperty("SelectionLanguage","XPath"); |
| /bookstore/book[last()] | Selects the last book element that is the child of the bookstore element |
| /bookstore/book[last()-1] | Selects the last but one book element that is the child of the bookstore element |
| /bookstore/book[position()<3] | Selects the first two book elements that are children of the bookstore element |
| //title[@lang] | Selects all the title elements that have an attribute named lang |
| //title[@lang='en'] | Selects all the title elements that have a "lang" attribute with a value of "en" |
| /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 |
| /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 |
Selección de nodos desconocidos
Los comodines XPath se pueden utilizar para seleccionar nodos XML desconocidos.
| Wildcard | Description |
|---|---|
| * | Matches any element node |
| @* | Matches any attribute node |
| node() | Matches any node of any kind |
En la siguiente tabla, hemos enumerado algunas expresiones de ruta y el resultado de las expresiones:
| Path Expression | Result |
|---|---|
| /bookstore/* | Selects all the child element nodes of the bookstore element |
| //* | Selects all elements in the document |
| //title[@*] | Selects all title elements which have at least one attribute of any kind |
Selección de varios caminos
Usando el | operador en una expresión XPath puede seleccionar varias rutas.
En la siguiente tabla, hemos enumerado algunas expresiones de ruta y el resultado de las expresiones:
| Path Expression | Result |
|---|---|
| //book/title | //book/price | Selects all the title AND price elements of all book elements |
| //title | //price | Selects all the title AND price elements in the document |
| /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 |