PHP: Uso básico de SimpleXML - Manual

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Uso básico de SimpleXML

Varios ejemplos de este capítulo requieren una cadena XML. En lugar de repetirla en cada ejemplo, se colocará en un archivo que se incluirá en cada uno de ellos. El contenido de este archivo se ilustra con el ejemplo que sigue. De lo contrario, puede crearse un documento XML y leerse con simplexml_load_file().

Ejemplo #1 Ejemplo de archivo incluido examples/simplexml-data.php con una cadena XML

<?php
$xmlstr = <<<XML
<?xml version='1.0' standalone='yes'?>
<movies>
 <movie>
  <title>PHP: Behind the Parser</title>
  <characters>
   <character>
    <name>Ms. Coder</name>
    <actor>Onlivia Actora</actor>
   </character>
   <character>
    <name>Mr. Coder</name>
    <actor>El Act&#211;r</actor>
   </character>
  </characters>
  <plot>
   So, this language. It's like, a programming language. Or is it a
   scripting language? All is revealed in this thrilling horror spoof
   of a documentary.
  </plot>
  <great-lines>
   <line>PHP solves all my web problems</line>
  </great-lines>
  <rating type="thumbs">7</rating>
  <rating type="stars">5</rating>
 </movie>
</movies>
XML;
?>

La simplicidad de SimpleXML se hace más evidente cuando se intenta extraer una cadena o un número de un documento XML básico.

Ejemplo #2 Lectura de <plot>

<?php
include 'examples/simplexml-data.php';

$movies = new SimpleXMLElement($xmlstr);

echo $movies->movie[0]->plot;
?>

El resultado del ejemplo sería:


   So, this language. It's like, a programming language. Or is it a
   scripting language? All is revealed in this thrilling horror spoof
   of a documentary.

El acceso a los elementos de un documento XML que contiene caracteres no permitidos según la convención de nombres de PHP (por ejemplo, palabras clave) es posible encapsulando el nombre del elemento entre corchetes y comillas simples.

Ejemplo #3 Recuperación de <line>

<?php
include 'examples/simplexml-data.php';

$movies = new SimpleXMLElement($xmlstr);

echo $movies->movie->{'great-lines'}->line;
?>

El resultado del ejemplo sería:

PHP solves all my web problems

Ejemplo #4 Acceder a un elemento no único con SimpleXML

Cuando existen múltiples instancias de un elemento como hijos de un elemento padre único, pueden aplicarse las técnicas normales de iteración.

<?php
include 'examples/simplexml-data.php';

$movies = new SimpleXMLElement($xmlstr);

/* Para cada <character>, se muestra un <name>. */
foreach ($movies->movie->characters->character as $character) {
   echo $character->name, ' played by ', $character->actor, PHP_EOL;
}

?>

El resultado del ejemplo sería:

Ms. Coder played by Onlivia Actora
Mr. Coder played by El ActÓr

Nota:
Las propiedades ($movies->movie en nuestro ejemplo anterior) no son arrays. Son objetos iterables y accesibles.

Ejemplo #5 Uso de atributos

Hasta ahora, solo se ha cubierto la lectura de los nombres de los elementos y sus valores. SimpleXML también puede acceder a sus atributos. El acceso a los atributos de un elemento se realiza de la misma manera que el acceso a los elementos de un array.

<?php
include 'examples/simplexml-data.php';

$movies = new SimpleXMLElement($xmlstr);

/* Acceso al nodo <rating> del primer <movie>.
 * Mostrar también los atributos de <rating>. */
foreach ($movies->movie[0]->rating as $rating) {
    switch((string) $rating['type']) { // Obtener atributos como índices de elementos
    case 'thumbs':
        echo $rating, ' thumbs up';
        break;
    case 'stars':
        echo $rating, ' stars';
        break;
    }
}
?>

El resultado del ejemplo sería:

7 thumbs up5 stars

Ejemplo #6 Comparación de elementos y atributos con texto

Para comparar un elemento o un atributo con una cadena de caracteres o para pasarlo a una función que requiera una cadena de caracteres, debe convertirse en una cadena utilizando (string). De lo contrario, PHP tratará el elemento como un objeto.

<?php
include 'examples/simplexml-data.php';

$movies = new SimpleXMLElement($xmlstr);

if ((string) $movies->movie->title == 'PHP: Behind the Parser') {
    print 'My favorite movie.';
}

echo htmlentities((string) $movies->movie->title);
?>

El resultado del ejemplo sería:

My favorite movie.PHP: Behind the Parser

Ejemplo #7 Comparación de 2 elementos

Dos objetos SimpleXMLElement se consideran diferentes incluso si apuntan al mismo elemento.

<?php
include 'examples/simplexml-data.php';

$movies1 = new SimpleXMLElement($xmlstr);
$movies2 = new SimpleXMLElement($xmlstr);
var_dump($movies1 == $movies2);
?>

El resultado del ejemplo sería:

bool(false)

Ejemplo #8 Uso de XPath

SimpleXML incluye soporte integrado para XPath. Para encontrar todos los elementos <character>.

'//' actúa como comodín. Para especificar una ruta absoluta, se elimina una barra.

<?php
include 'examples/simplexml-data.php';

$movies = new SimpleXMLElement($xmlstr);

foreach ($movies->xpath('//character') as $character) {
    echo $character->name, ' played by ', $character->actor, PHP_EOL;
}
?>

El resultado del ejemplo sería:

Ms. Coder played by Onlivia Actora
Mr. Coder played by El ActÓr

Ejemplo #9 Asignación de valores

Los datos en SimpleXML no tienen que ser constantes. El objeto permite la manipulación de todos estos elementos.

<?php
include 'examples/simplexml-data.php';
$movies = new SimpleXMLElement($xmlstr);

$movies->movie[0]->characters->character[0]->name = 'Miss Coder';

echo $movies->asXML();
?>

El resultado del ejemplo sería:

<?xml version="1.0" standalone="yes"?>
<movies>
 <movie>
  <title>PHP: Behind the Parser</title>
  <characters>
   <character>
    <name>Miss Coder</name>
    <actor>Onlivia Actora</actor>
   </character>
   <character>
    <name>Mr. Coder</name>
    <actor>El Act&#xD3;r</actor>
   </character>
  </characters>
  <plot>
   So, this language. It's like, a programming language. Or is it a
   scripting language? All is revealed in this thrilling horror spoof
   of a documentary.
  </plot>
  <great-lines>
   <line>PHP solves all my web problems</line>
  </great-lines>
  <rating type="thumbs">7</rating>
  <rating type="stars">5</rating>
 </movie>
</movies>

Ejemplo #10 Añadir elementos y atributos

SimpleXML es capaz de añadir fácilmente hijos y atributos.

<?php
include 'examples/simplexml-data.php';
$movies = new SimpleXMLElement($xmlstr);

$character = $movies->movie[0]->characters->addChild('character');
$character->addChild('name', 'Mr. Parser');
$character->addChild('actor', 'John Doe');

$rating = $movies->movie[0]->addChild('rating', 'PG');
$rating->addAttribute('type', 'mpaa');

echo $movies->asXML();
?>

El resultado del ejemplo sería:

<?xml version="1.0" standalone="yes"?>
<movies>
 <movie>
  <title>PHP: Behind the Parser</title>
  <characters>
   <character>
    <name>Ms. Coder</name>
    <actor>Onlivia Actora</actor>
   </character>
   <character>
    <name>Mr. Coder</name>
    <actor>El Act&#xD3;r</actor>
   </character>
  <character><name>Mr. Parser</name><actor>John Doe</actor></character></characters>
  <plot>
   So, this language. It's like, a programming language. Or is it a
   scripting language? All is revealed in this thrilling horror spoof
   of a documentary.
  </plot>
  <great-lines>
   <line>PHP solves all my web problems</line>
  </great-lines>
  <rating type="thumbs">7</rating>
  <rating type="stars">5</rating>
 <rating type="mpaa">PG</rating></movie>
</movies>

Ejemplo #11 Interoperabilidad DOM

PHP tiene un mecanismo para convertir nodos XML entre los formatos SimpleXML y DOM. Este ejemplo muestra cómo cambiar un elemento DOM a SimpleXML.

<?php
$dom = new DOMDocument;
$dom->loadXML('<books><book><title>blah</title></book></books>');
if (!$dom) {
    echo 'Error al analizar el documento';
    exit;
}

$books = simplexml_import_dom($dom);

echo $books->book[0]->title;
?>

El resultado del ejemplo sería:

blah

Ejemplo #12 Uso de espacios de nombres

<?php
$data = <<<XML
<movies xmlns="http://default" xmlns:a="http://a">
 <movie xml:id="movie1" a:link="IMDB">
  <a:actor>Onlivia Actora</a:actor>
 </movie>
</movies>
XML;

$movies = simplexml_load_string($data);

// El espacio de nombres http://www.w3.org/XML/1998/namespace está disponible bajo el nombre "xml".
echo $movies->movie->attributes("xml", true)["id"] . "\n";

// Los atributos con espacio de nombres pueden recuperarse con attributes().
echo $movies->movie->attributes("a", true)["link"] . "\n";

// El uso de la URI del espacio de nombres permite usar cualquier alias en el documento.
echo $movies->movie->attributes("http://a")["link"] . "\n";

// Los hijos pueden recuperarse con children().
echo $movies->movie->children("http://a")->actor . "\n";

// El uso de xpath() con un espacio de nombres requiere registrarlo primero.
$movies->registerXPathNamespace("a", "http://a");
echo count($movies->xpath("//a:actor")) . "\n";

// Incluso el espacio de nombres por defecto debe registrarse.
$movies->registerXPathNamespace("default", "http://default");
echo count($movies->xpath("//default:movie")) . "\n";

// Esto está vacío.
echo count($movies->xpath("//movie")) . "\n";
?>

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User Contributed Notes 9 notes

up

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87

rowan dot collins at gmail dot com ¶

10 years ago

There is a common "trick" often proposed to convert a SimpleXML object to an array, by running it through json_encode() and then json_decode(). I'd like to explain why this is a bad idea.

Most simply, because the whole point of SimpleXML is to be easier to use and more powerful than a plain array. For instance, you can write <?php $foo->bar->baz['bing'] ?> and it means the same thing as <?php $foo->bar[0]->baz[0]['bing'] ?>, regardless of how many bar or baz elements there are in the XML; and if you write <?php (string)$foo->bar[0]->baz[0] ?> you get all the string content of that node - including CDATA sections - regardless of whether it also has child elements or attributes. You also have access to namespace information, the ability to make simple edits to the XML, and even the ability to "import" into a DOM object, for much more powerful manipulation. All of this is lost by turning the object into an array rather than reading understanding the examples on this page.

Additionally, because it is not designed for this purpose, the conversion to JSON and back will actually lose information in some situations. For instance, any elements or attributes in a namespace will simply be discarded, and any text content will be discarded if an element also has children or attributes. Sometimes, this won't matter, but if you get in the habit of converting everything to arrays, it's going to sting you eventually.

Of course, you could write a smarter conversion, which didn't have these limitations, but at that point, you are getting no value out of SimpleXML at all, and should just use the lower level XML Parser functions, or the XMLReader class, to create your structure. You still won't have the extra convenience functionality of SimpleXML, but that's your loss.

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65

jishcem at gmail dot com ¶

12 years ago

For me it was easier to use arrays than objects, 

So, I used this code, 

$xml = simplexml_load_file('xml_file.xml');
    
$json_string = json_encode($xml);
    
$result_array = json_decode($json_string, TRUE);

Hope it would help someone

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13

Anonymous ¶

7 years ago

If your xml string contains booleans encoded with "0" and "1", you will run into problems when you cast the element directly to bool:

$xmlstr = <<<XML
<?xml version='1.0' standalone='yes'?>
<values>
    <truevalue>1</truevalue>
    <falsevalue>0</falsevalue>
</values>
XML;
$values = new SimpleXMLElement($xmlstr);
$truevalue = (bool)$values->truevalue; // true
$falsevalue = (bool)$values->falsevalue; // also true!!!

Instead you need to cast to string or int first:

$truevalue = (bool)(int)$values->truevalue; // true
$falsevalue = (bool)(int)$values->falsevalue; // false

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3

3 years ago

How to find out if a Node exists:

<?xml version='1.0' standalone='yes'?>
<book>
  <author>Josef</author>
  <isbn></isbn>
</book>

empty($xml->isbn) will be true
isset($xml->isbn) will be true

empty($xml->title) will be true
isset($xml->title) will be false

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16

ie dot raymond at gmail dot com ¶

15 years ago

If you need to output valid xml in your response, don't forget to set your header content type to xml in addition to echoing out the result of asXML():



<?php



$xml=simplexml_load_file('...');

...

...xml stuff

...



//output xml in your response:

header('Content-Type: text/xml');

echo $xml->asXML();

?>

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10

gkokmdam at zonnet dot nl ¶

14 years ago

A quick tip on xpath queries and default namespaces. It looks like the XML-system behind SimpleXML has the same workings as I believe the XML-system .NET uses: when one needs to address something in the default namespace, one will have to declare the namespace using registerXPathNamespace and then use its prefix to address the otherwise in the default namespace living element.

<?php
$string = <<<XML
<?xml version='1.0'?> 
<document xmlns="http://www.w3.org/2005/Atom">
 <title>Forty What?</title>
 <from>Joe</from>
 <to>Jane</to>
 <body>
  I know that's the answer -- but what's the question?
 </body>
</document>
XML;

$xml = simplexml_load_string($string);
$xml->registerXPathNamespace("def", "http://www.w3.org/2005/Atom");

$nodes = $xml->xpath("//def:document/def:title");

?>

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8

14 years ago

Using stuff like: is_object($xml->module->admin) to check if there actually is a node called "admin", doesn't seem to work as expected, since simplexml always returns an object- in that case an empty one  - even if a particular node does not exist. 
For me good old empty() function seems to work just fine in such cases.

Cheers

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4

Max K. ¶

15 years ago

From the README file:

SimpleXML is meant to be an easy way to access XML data.

SimpleXML objects follow four basic rules:

1) properties denote element iterators
2) numeric indices denote elements
3) non numeric indices denote attributes
4) string conversion allows to access TEXT data

When iterating properties then the extension always iterates over
all nodes with that element name. Thus method children() must be 
called to iterate over subnodes. But also doing the following:
foreach ($obj->node_name as $elem) {
  // do something with $elem
}
always results in iteration of 'node_name' elements. So no further 
check is needed to distinguish the number of nodes of that type.

When an elements TEXT data is being accessed through a property
then the result does not include the TEXT data of subelements.

Known issues
============

Due to engine problems it is currently not possible to access
a subelement by index 0: $object->property[0].

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1

php at keith tyler dot com ¶

15 years ago

[Editor's Note: The SimpleXMLIterator class, however, does implement these methods.]



While SimpleXMLElement claims to be iterable, it does not seem to implement the standard Iterator interface functions like ::next and ::reset properly. Therefore while foreach() works, functions like next(), current(), or each() don't seem to work as you would expect -- the pointer never seems to move or keeps getting reset.