PHP Tutorial: May 2013

PHP SimpleXML

What is SimpleXML?

SimpleXML is new in PHP 5. It is an easy way of getting an element's attributes and text, if you know the XML document's layout.
Compared to DOM or the Expat parser, SimpleXML just takes a few lines of code to read text data from an element.
SimpleXML converts the XML document into an object, like this:

Elements - Are converted to single attributes of the SimpleXMLElement object. When there's more than one element on one level, they're placed inside an array
Attributes - Are accessed using associative arrays, where an index corresponds to the attribute name
Element Data - Text data from elements are converted to strings. If an element has more than one text node, they will be arranged in the order they are found

SimpleXML is fast and easy to use when performing basic tasks like:

Reading XML files
Extracting data from XML strings
Editing text nodes or attributes

However, when dealing with advanced XML, like namespaces, you are better off using the Expat parser or the XML DOM.

Installation

As of PHP 5.0, the SimpleXML functions are part of the PHP core. There is no installation needed to use these functions.

Using SimpleXML

Below is an XML file:

<?xml version="1.0" encoding="ISO-8859-1"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

We want to output the element names and data from the XML file above.
Here's what to do:

Load the XML file
Get the name of the first element
Create a loop that will trigger on each child node, using the children() function
Output the element name and data for each child node

Example

<?php
$xml = simplexml_load_file("test.xml");

echo $xml->getName() . " ";

foreach($xml->children() as $child)
 {
 echo $child->getName() . ": " . $child . " ";
 }
?>

The output of the code above will be:

note
to: Tove
from: Jani
heading: Reminder
body: Don't forget me this weekend!

What is DOM?

The W3C DOM provides a standard set of objects for HTML and XML documents, and a standard interface for accessing and manipulating them.

The W3C DOM is separated into different parts (Core, XML, and HTML) and different levels (DOM Level 1/2/3):

* Core DOM - defines a standard set of objects for any structured document
* XML DOM - defines a standard set of objects for XML documents
* HTML DOM - defines a standard set of objects for HTML documents

If you want to learn more about the XML DOM, please visit our XML DOM tutorial.

XML Parsing

To read and update - create and manipulate - an XML document, you will need an XML parser.
There are two basic types of XML parsers:

Tree-based parser: This parser transforms an XML document into a tree structure. It analyzes the whole document, and provides access to the tree elements
Event-based parser: Views an XML document as a series of events. When a specific event occurs, it calls a function to handle it

The DOM parser is an tree-based parser.
Look at the following XML document fraction:

<?xml version="1.0" encoding="ISO-8859-1"?>
<from>Jani</from>

The XML DOM sees the XML above as a tree structure:

Level 1: XML Document
Level 2: Root element: <from>
Level 3: Text element: "Jani"

Installation

The DOM XML parser functions are part of the PHP core. There is no installation needed to use these functions.

An XML File

The XML file below will be used in our example:

<?xml version="1.0" encoding="ISO-8859-1"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

Load and Output XML

We want to initialize the XML parser, load the xml, and output it:

Example

<?php
$xmlDoc = new DOMDocument();
$xmlDoc->load("note.xml");

print $xmlDoc->saveXML();
?>

The output of the code above will be:

Tove Jani Reminder Don't forget me this weekend!

If you select "View source" in the browser window, you will see the following HTML:

<?xml version="1.0" encoding="ISO-8859-1"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

The example above creates a DOMDocument-Object and loads the XML from "note.xml" into it.
Then the saveXML() function puts the internal XML document into a string, so we can output it.

Looping through XML

We want to initialize the XML parser, load the XML, and loop through all elements of the <note> element:

Example

<?php
$xmlDoc = new DOMDocument();
$xmlDoc->load("note.xml");

$x = $xmlDoc->documentElement;
foreach ($x->childNodes AS $item)
 {
 print $item->nodeName . " = " . $item->nodeValue . " ";
 }
?>

The output of the code above will be:

#text =
to = Tove
#text =
from = Jani
#text =
heading = Reminder
#text =
body = Don't forget me this weekend!
#text =

In the example above you see that there are empty text nodes between each element.
When XML generates, it often contains white-spaces between the nodes. The XML DOM parser treats these as ordinary elements, and if you are not aware of them, they sometimes cause problems.

PHP XML Expat Parser

The built-in Expat parser makes it possible to process XML documents in PHP.

What is XML?

XML is used to describe data and to focus on what data is. An XML file describes the structure of the data.
In XML, no tags are predefined. You must define your own tags.

What is Expat?

To read and update - create and manipulate - an XML document, you will need an XML parser.
There are two basic types of XML parsers:

Tree-based parser: This parser transforms an XML document into a tree structure. It analyzes the whole document, and provides access to the tree elements. e.g. the Document Object Model (DOM)
Event-based parser: Views an XML document as a series of events. When a specific event occurs, it calls a function to handle it

The Expat parser is an event-based parser.
Event-based parsers focus on the content of the XML documents, not their structure. Because of this, event-based parsers can access data faster than tree-based parsers.
Look at the following XML fraction:

An event-based parser reports the XML above as a series of three events:

Start element: from
Start CDATA section, value: Jani
Close element: from

The XML example above contains well-formed XML. However, the example is not valid XML, because there is no Document Type Definition (DTD) associated with it.
However, this makes no difference when using the Expat parser. Expat is a non-validating parser, and ignores any DTDs.
As an event-based, non-validating XML parser, Expat is fast and small, and a perfect match for PHP web applications.
Note: XML documents must be well-formed or Expat will generate an error.

Installation

The XML Expat parser functions are part of the PHP core. There is no installation needed to use these functions

An XML File

The XML file below will be used in our example:

<?xml version="1.0" encoding="ISO-8859-1"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

Initializing the XML Parser

We want to initialize the XML parser in PHP, define some handlers for different XML events, and then parse the XML file.

Example

<?php
//Initialize the XML parser
$parser=xml_parser_create();

//Function to use at the start of an element
function start($parser,$element_name,$element_attrs)
 {
 switch($element_name)
 {
 case "NOTE":
 echo "-- Note -- ";
 break;
 case "TO":
 echo "To: ";
 break;
 case "FROM":
 echo "From: ";
 break;
 case "HEADING":
 echo "Heading: ";
 break;
 case "BODY":
 echo "Message: ";
 }
 }

//Function to use at the end of an element
function stop($parser,$element_name)
 {
 echo " ";
 }

//Function to use when finding character data
function char($parser,$data)
 {
 echo $data;
 }

//Specify element handler
xml_set_element_handler($parser,"start","stop");

//Specify data handler
xml_set_character_data_handler($parser,"char");

//Open XML file
$fp=fopen("test.xml","r");

//Read data
while ($data=fread($fp,4096))
 {
 xml_parse($parser,$data,feof($fp)) or
 die (sprintf("XML Error: %s at line %d",
 xml_error_string(xml_get_error_code($parser)),
 xml_get_current_line_number($parser)));
 }

//Free the XML parser
xml_parser_free($parser);
?>

The output of the code above will be:

-- Note --
To: Tove
From: Jani
Heading: Reminder
Message: Don't forget me this weekend!

How it works:

Initialize the XML parser with the xml_parser_create() function
Create functions to use with the different event handlers
Add the xml_set_element_handler() function to specify which function will be executed when the parser encounters the opening and closing tags
Add the xml_set_character_data_handler() function to specify which function will execute when the parser encounters character data
Parse the file "test.xml" with the xml_parse() function
In case of an error, add xml_error_string() function to convert an XML error to a textual description

Call the xml_parser_free() function to release the memory allocated with the xml_parser_create() function

PHP Tutorial

Wednesday 29 May 2013

PHP SimpleXML

What is SimpleXML?

Installation

Using SimpleXML

What is DOM?

XML Parsing

Installation

An XML File

Load and Output XML

Example

Looping through XML

Example

PHP XML Expat Parser

What is XML?

What is Expat?

Installation

An XML File

Initializing the XML Parser

Example

Simple CRUD in Laravel Framework

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