XPath- sintaksis
XPath gebruik paduitdrukkings om nodusse of nodusstelle in 'n XML-dokument te kies. Die nodus word gekies deur 'n pad of stappe te volg.
Die XML-voorbeelddokument
Ons sal die volgende XML-dokument in die voorbeelde hieronder gebruik.
<?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>
Kies nodusse
XPath gebruik paduitdrukkings om nodusse in 'n XML-dokument te kies. Die nodus word gekies deur 'n pad of stappe te volg. Die nuttigste paduitdrukkings word hieronder gelys:
| 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 |
In die tabel hieronder het ons 'n paar paduitdrukkings en die resultaat van die uitdrukkings gelys:
| 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 |
Predikate
Predikate word gebruik om 'n spesifieke nodus of 'n nodus wat 'n spesifieke waarde bevat te vind.
Predikate is altyd tussen vierkantige hakies ingebed.
In die tabel hieronder het ons 'n paar paduitdrukkings met predikate en die resultaat van die uitdrukkings gelys:
| 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 |
Kies onbekende nodes
XPath-jokertekens kan gebruik word om onbekende XML-nodes te kies.
| Wildcard | Description |
|---|---|
| * | Matches any element node |
| @* | Matches any attribute node |
| node() | Matches any node of any kind |
In die tabel hieronder het ons 'n paar paduitdrukkings en die resultaat van die uitdrukkings gelys:
| 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 |
Kies verskeie paaie
Deur die gebruik van die | operateur in 'n XPath uitdrukking kan jy verskeie paaie kies.
In die tabel hieronder het ons 'n paar paduitdrukkings en die resultaat van die uitdrukkings gelys:
| 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 |