Using a few additional methods: finding child nodes, accessing attributes and using the XML DOM - PHP

As I said in the previous section, the “simpleXML” extension comes with some additional methods for parsing XML data, which can be quite useful, depending on the requirements of your PHP 5 applications.

The first method that I’ll explain is called “children()”, and as its name suggests, is aimed at finding all the child nodes of a parent element. To clarify how it can be used, I’ll use the following XML data string:

$xmlstr=<<<XML
<?xml version="1.0" encoding="iso-8859-1"?>
<users>
<user>
<name>John Doe</name>
<address>Binary Avenue 1234 FL</address>
<email>john@domain.com</email>
<gender>
<type>Male</type>
</gender>
</user>
<user>
<name>Janet Smith</name>
<address>Crazy Bits Road 4568 CA</address>
<email>janet@janet-domain.com</email>
<gender>
<type>Female</type>
</gender>
</user>
</users>
XML;

As you can see, I created a new string of XML data, so you can have an accurate idea of how to access the child nodes of all the <gender> nodes. Now, take a look at the following script, which uses the “children()” method for performing this task:

// example finding child nodes of <gender> nodes with the
children() method
require_once 'xml_string.php';
if(!$xml=simplexml_load_string($xmlstr)){
    trigger_error('Error reading XML string',E_USER_ERROR);
}
foreach($xml->children() as $children){
    echo 'Name node found with the following value: '.$children-
>name.'<br />';
    foreach($children->children() as $newchildren){
        if($newchildren->type!=''){
            echo 'Gender node has the following child node:
'.$newchildren->type.'<br />';
        }
    }
}

On this occasion, the above script utilizes the “children()” method inside two “foreach” loops, in order to find all the child nodes that belong to the corresponding <gender> elements, which outputs the following result:

Name node found with the following value: John Doe
Gender node has the following child node: Male
Name node found with the following value: Janet Smith
Gender node has the following child node: Female

Well, if the previous example is a little bit harder to understand, check out this one, which uses the following XML string and certainly is much simpler to read and code:

$xmlstr=<<<XML
<?xml version="1.0" encoding="iso-8859-1"?>
<users>
<user>
<name>John Doe</name>
<address>Binary Avenue 1234 FL</address>
<email>john@john-domain.com</email>
<gender type="male">1</gender>
<gender type="female">2</gender>
</user>
<user>
<name>Janet Smith</name>
<address>Crazy Bits Road 4568 CA</address>
<email>janet@janet-domain.com</email>
<gender type="male">1</gender>
<gender type="female">2</gender>
</user>
<user>
<name>James Smith</name>
<address>Socket Boulevard 7894 OH</address>
<email>james@james-domain.com</email>
<gender type="male">1</gender>
<gender type="female">2</gender>
</user>
<user>
<name>Silvia Wilson</name>
<address>Protocol Avenue 5652 NY</address>
<email>silvia@silvia-domain.com</email>
<gender type="male">1</gender>
<gender type="female">2</gender>
</user>
<user>
<name>Alejandro Gervasio</name>
<address>Boulevard of Objects 10101 AR</address>
<email>alejandro@alejandro-domain.com</email>
<gender type="male">1</gender>
<gender type="female">2</gender>
</user>
</users>
XML;

require_once 'xml_string.php';
if(!$xml=simplexml_load_string($xmlstr)){
    trigger_error('Error reading XML string',E_USER_ERROR);
}
foreach($xml->children() as $children){
    echo 'Name node with the following value '.$children->name.'<br />';
}

// displays the following output

Name node with the following value John Doe
Name node with the following value Janet Smith
Name node with the following value James Smith
Name node with the following value Silvia Wilson
Name node with the following value Alejandro Gervasio

Actually, the example shown above is rather trivial, but I just want you to grasp correctly the logic behind the “children()” method. Did you get it? I hope so.

Finally, the two methods that I’d like to show you are called “attributes()” and “simple_import_dom()” respectively. Obviously, the first one is focused on retrieving all the attributes that correspond to a specific XML node, while the second one is useful for importing a new DOM document as XML data.

With reference to the “attributes()” method, here is an example that teaches you how it can be implemented:

$xmlstr=<<<XML
<?xml version="1.0" encoding="iso-8859-1"?>
<users>
<user name="John Doe" address="Binary Avenue 1234 FL" email="john@john-domain.com">User1</user>
<user name="Janet Smith" address="Crazy Bits Road 4568 CA" email="janet@janet-domain.com">User2</user>
</users>
XML;

// example using the 'attributes()' method
require_once 'xml_string.php';
if(!$xml=simplexml_load_string($xmlstr)){
    trigger_error('Error reading XML string',E_USER_ERROR);
}
foreach($xml->user[0]->attributes() as $attr=>$value){
    echo 'Attribute '.$attr. ' found with the following value: '.$value.'<br />';
}

// displays the following output

Attribute name found with the following value: John Doe
Attribute address found with the following value: Binary Avenue
1234 FL
Attribute email found with the following value: john@john-
domain.com

As you can see, the “attributes()” method allows you to obtain all the attributes of a particular element within a XML string, which are returned as an associative array. In this case, I used basic XML data, so that you can easily understand how this method works.

After demonstrating how the “attributes()” method does its thing, take a little break and examine the code snippet below, which shows how to implement the “simplexml_import_dom()” method:

// example using the 'import_dom()' method
$dom=new domDocument;
if(!$dom->loadXML('<users><user><name>John
Doe</name><address>Binary Avenue 1234
FL</address><email>ohn@john-domain.com</email></user></users>')){
    trigger_error('Error loading XML string',E_USER_ERROR);
}
$xml=simplexml_import_dom($dom);
echo 'Name of first user: '.$xml->user[0]->name;

// displays the following output

Name of first user: John Doe

I purposely kept the above example rather simple, since the XML DOM is a huge topic, and certainly is out of the scope of this series. In short, the “simplexml_import_dom()” method can be used as an alternative way to load XML data strings onto an object. It lets you obtain results similar to using both the “simplexml_load_file()” and “simplexml_load_string()” methods. However, if you want to take the shortest path to parsing XML data, I suggest you to use these methods instead.

Wrapping up

Finally, we’re done. Over the course of this series, I introduced some of the most important functions that are included within the “simpleXML” PHP 5 extension. As you saw, this library eventually might fit the requirements of many applications that don’t demand complex parsing of XML data. If your next PHP-driven project falls under this category, go ahead and use it with no restrictions. See you in the next PHP tutorial!