Leveraging XML with PHPs SimpleXML Library

SimpleXML is a powerful library which converts XML strings to an easy to use PHP object.

The following assumes an XML structure as below.

<?xml version="1.0" encoding="UTF-8"?>
<document>
    <book>
        <bookName>StackOverflow SimpleXML Example</bookName>
        <bookAuthor>PHP Programmer</bookAuthor>
    </book>
    <book>
        <bookName>Another SimpleXML Example</bookName>
        <bookAuthor>Stack Overflow Community</bookAuthor>
        <bookAuthor>PHP Programmer</bookAuthor>
        <bookAuthor>FooBar</bookAuthor>
    </book>
</document>

Read our data in to SimpleXML

To get started, we need to read our data into SimpleXML. We can do this in 3 different ways. Firstly, we can load our data from a DOM node.

$xmlElement = simplexml_import_dom($domNode);

Our next option is to load our data from an XML file.

$xmlElement = simplexml_load_file($filename);

Lastly, we can load our data from a variable.

$xmlString = '<?xml version="1.0" encoding="UTF-8"?>
<document>
    <book>
        <bookName>StackOverflow SimpleXML Example</bookName>
        <bookAuthor>PHP Programmer</bookAuthor>
    </book>
    <book>
        <bookName>Another SimpleXML Example</bookName>
        <bookAuthor>Stack Overflow Community</bookAuthor>
        <bookAuthor>PHP Programmer</bookAuthor>
        <bookAuthor>FooBar</bookAuthor>
    </book>
</document>';
$xmlElement = simplexml_load_string($xmlString);

Whether you’ve picked to load from a DOM Element, from a file or from a string, you are now left with a SimpleXMLElement variable called $xmlElement. Now, we can start to make use of our XML in PHP.

Accessing our SimpleXML Data

The simplest way to access data in our SimpleXMLElement object is to call the properties directly. If we want to access our first bookName, StackOverflow SimpleXML Example, then we can access it as per below.

echo $xmlElement->book->bookName;

At this point, SimpleXML will assume that because we have not told it explicitly which book we want, that we want the first one. However, if we decide that we do not want the first one, rather that we want Another SimpleXML Example, then we can access it as per below.

echo $xmlElement->book[1]->bookName;

It is worth noting that using [0] works the same as not using it, so

$xmlElement->book

works the same as

$xmlElement->book[0]

Looping through our XML

There are many reasons you may wish to loop through XML, such as that you have a number of items, books in our case, that we would like to display on a webpage. For this, we can use a foreach loop or a standard for loop, taking advantage of SimpleXMLElement’s count function..

foreach ( $xmlElement->book as $thisBook ) {
    echo $thisBook->bookName
}

$count = $xmlElement->count();
for ( $i=0; $i<$count; $i++ ) {
    echo $xmlElement->book[$i]->bookName;
}

Handling Errors

Now we have come so far, it is important to realise that we are only humans, and will likely encounter an error eventually - especially if we are playing with different XML files all the time. And so, we will want to handle those errors.

Consider we created an XML file. You will notice that while this XML is much alike what we had earlier, the problem with this XML file is that the final closing tag is /doc instead of /document.

<?xml version="1.0" encoding="UTF-8"?>
<document>
    <book>
        <bookName>StackOverflow SimpleXML Example</bookName>
        <bookAuthor>PHP Programmer</bookAuthor>
    </book>
    <book>
        <bookName>Another SimpleXML Example</bookName>
        <bookAuthor>Stack Overflow Community</bookAuthor>
        <bookAuthor>PHP Programmer</bookAuthor>
        <bookAuthor>FooBar</bookAuthor>
    </book>
</doc>

Now, say, we load this into our PHP as $file.

libxml_use_internal_errors(true);
$xmlElement = simplexml_load_file($file);
if ( $xmlElement === false ) {
    $errors = libxml_get_errors();
    foreach ( $errors as $thisError ) {
        switch ( $thisError->level ) {
            case LIBXML_ERR_FATAL:
                echo "FATAL ERROR: ";
                break;
            case LIBXML_ERR_ERROR:
                echo "Non Fatal Error: ";
                break;
            case LIBXML_ERR_WARNING:
                echo "Warning: ";
                break;
        }
        echo $thisError->code . PHP_EOL .
            'Message: ' . $thisError->message . PHP_EOL .
            'Line: ' . $thisError->line . PHP_EOL .
            'Column: ' . $thisError->column . PHP_EOL .
            'File: ' . $thisError->file;
    }
    libxml_clear_errors();
} else {
    echo 'Happy Days';
}

We will be greeted with the following

FATAL ERROR: 76
Message: Opening and ending tag mismatch: document line 2 and doc

Line: 13
Column: 10
File: filepath/filename.xml

However as soon as we fix this problem, we are presented with “Happy Days”.

Found a mistake? Have a question or improvement idea? Let me know.

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