DOM guide: Importing documents

Be sure to read the section on creating documents first. It covers some important topics relevant to this section.

A simple example

Let's begin with a simple example of reading some information from a Collada document. We'll open the document and print the ID of the first <node> we find.

DAE dae;
daeElement* root = dae.open("simpleImport.dae");
if (!root) {
    cout << "Document import failed.\n";
    return 0;
}

We create the DAE object then call DAE::open to open a file called "simpleImport.dae". If there is no file of that name in the current directory, or the file failed to open for some other reason, then the DAE::open method will return null. We check for that and print an error message if opening the document failed.

daeElement* node = root->getDescendant("node");
if (!node)
    cout << "No nodes found\n";
else
    cout << "node id: " << node->getAttribute("id") << endl;

Here we use the daeElement::getDescendant method to do a breadth-first search through the xml element tree for an element with the given name. This method will return null if it couldn't find an element with a matching name, which we check for. If it did find a matching element we use the daeElement::getAttribute method to print the value of the 'id' attribute.

The complete code.

#include <iostream>
#include <dae.h>
#include <dom/domCOLLADA.h>
using namespace std;

int main() {
	DAE dae;
	daeElement* root = dae.open("simpleImport.dae");
	if (!root) {
		cout << "Document import failed.\n";
		return 0;
	}

	daeElement* node = root->getDescendant("node");
	if (!node)
		cout << "No nodes found\n";
	else
		cout << "node id: " << node->getAttribute("id") << endl;

	return 0;
}

The simpleImport.dae document.

<?xml version="1.0" encoding="UTF-8"?>
<COLLADA xmlns="http://www.collada.org/2005/11/COLLADASchema" version="1.4.1">
	<asset>
		<contributor/>
		<created>2008-04-08T13:07:52-08:00</created>
		<modified>2008-04-08T13:07:52-08:00</modified>
	</asset>
  <library_nodes>
    <node id="hello"/>
  </library_nodes>
</COLLADA>

And the results of running the program.

node id: hello

Reading data from elements

Any individual xml element has three types of data you might need: the element name, the element's attributes, and the element's character data. The DOM provides easy access to all of this data via the daeElement interface.

Element name

Use the daeElement::getElementName method to get an element's name.

daeString getElementName() const; // Function signature

cout << elt->getElementName() << endl; // Example: print an element's name

Element attributes

To get the value of an attribute given the attribute's name, use the daeElement::getAttribute method.

std::string getAttribute(daeString name);

We've already seen an example of daeElement::getAttribute usage in the simple import example.

cout << "node id: " << node->getAttribute("id") << endl;

If you don't know what attributes an element has, you can iterate over its attribute list using the following methods of daeElement.

size_t getAttributeCount();
std::string getAttributeName(size_t i);
std::string getAttribute(size_t i);

This code snippet prints all the attribute names and values of the root element.

for (size_t i = 0; i < root->getAttributeCount(); i++) {
	cout << "attr " << i << " name: " << root->getAttributeName(i) << endl;
	cout << "attr " << i << " value: " << root->getAttribute(i) << endl;
}