SimpleXML: Selecting Elements Which Have A Certain Attribute Value

Question

In an XML document, I have elements which share the same name, but the value of an attribute defines what type of data it is, and I want to select all of those elements which have a certain value from the document. Do I need to use XPath (and if so, could you suggest the right syntax) or is there a more elegant solution?

Here's some example XML:

<object>
  <data type="me">myname</data>
  <data type="you">yourname</data>
  <data type="me">myothername</data>
</object>

And I want to select the contents of all <data> tags children of <object> who's type is me.

PS - I'm trying to interface with the Netflix API using PHP - this shouldn't matter for my question, but if you want to suggest a good/better way to do so, I'm all ears.

Solution 1

Try this XPath:

/object/data[@type="me"]

Which reads as:

• Select (/) children of the current element called object
• Select (/) their children called data
• Filter ([...]) that list to elements where ...
  • the attribute type (the @ means "attribute")
  • has the text value me

So:

$myDataObjects = $simplexml->xpath('/object/data[@type="me"]');

If object is not the root of your document, you might want to use //object/data[@type="me"] instead. The // means "find all descendents" rather than "find all children".

Solution 2

I just made a function to do this for me; it only grabs the first result though. Your mileage may vary.

function query_attribute($xmlNode, $attr_name, $attr_value) {
  foreach($xmlNode as $node) { 
    if($node[$attr_name] == $attr_value) {
        return $node;
    }
  }
}

Usage:

echo query_attribute($MySimpleXmlNode->Customer, "type", "human")->Name;

(For the XML below)

<Root><Customer type="human"><Name>Sam Jones</name></Customer></Root>

Comments

[Ar5hv1r]

Why not use the XPath Gumbo suggested? And why use a switch instead of the easier to read if($node[$attr_name] == $attr_value)?

[IMSoP]

This is a useful example to have, because sometimes you want to incorporate additional logic, so that XPath isn't the best approach.

[Austin Burk]

Can this be done when the element has a default xmlns?