XML Filtering

XML Filtering

Arguably, the most powerful and useful feature of E4X is its ability to filter data. This new feature replaces the need for XPath libraries and the loops previously used to search an XML document in earlier versions of ActionScript. Now you can do all this natively in ActionScript 3.0 using as little as one line of code.

To use filtering, you can enclose expressions in parentheses as part of an E4X expression. The following examples show a few uses of filtering. We'll use the same XML object for all our examples:

var catalog:XML = <catalog>
   <product id="0">
      <name>Product One</name>
      <price>50</price>
   </product>
   <product id="1">
      <name>Product Two</name>
      <price>35</price>
   </product>
</catalog>;

The following line retrieves the product element that has an id attribute equal to 1. This example returns just one XML object, but it would return an XMLList if more than one element matches the criteria.

var product1:XML = catalog.product.(@id == 1);

This next line grabs the name of the product element that has a price less than 50. It's important to understand that this would return an XMLList if more than one element met the criteria:

var cheapestProductName:String = catalog.product.(price < 50).name;

This example retrieves the product elements that have a price greater than 35 and less than 50:

var productRange:XMLList = catalog.product.(price >= 35 && price <= 50);

Iterating Through an XMLList

Developers must often iterate , or loop, through an XMLList object. ActionScript 3.0 provides a few ways to do this. We'll use the same catalog example to demonstrate three different ways to iterate through the products and add up the price values. Here again is the literal syntax for creating the catalog object:

var catalog:XML = <catalog>
   <product id="0">
      <name>Product One</name>
      <price>50</price>
   </product>
   <product id="1">
      <name>Product Two</name>
      <price>35</price>
   </product>
</catalog>;

var total:Number = 0;
for(var i:int = 0; i < catalog.product.length(); i++) {
   total += (catalog.product[i].price as Number);

}

var total:Number = 0;
for(var i:String in catalog.product) {
total += (catalog.product[i].price as Number);
}

var total:Number = 0;
for each(var product:XML in catalog.product) {
   total += (product.price as Number);
}

var product:XML = <product id="0" name="Product One" price="50" />;
for each(var attribute:XML in product.@*) {
   trace(attribute.name() + ": " + attribute.toXMLString());
}