Feature attributes are not serialized to KML format

[towa48]

Feature attributes are not serialized to KML format. Method OpenLayers.Format.KML.createPlacemarkXML() serialize only name, description and geometry. But i have portion of ExtendedData in my features. Method OpenLayers.Format.KML.parseExtendedData() deserialize Data and SimpleData elemnts to objects and do not make a difference between them.

http://code.google.com/apis/kml/documentation/kmlreference.html#extendeddata
How can I choose between Data and SimpleData?
This code serialize to Data by default.

OpenLayers.Format.KML.prototype.createPlacemarkXML = function (feature) {
    var placemarkNode = this.createElementNS(this.kmlns, "Placemark"),
        placemarkName = this.createElementNS(this.kmlns, "name"),
        placemarkDesc = this.createElementNS(this.kmlns, "description"),
        name, desc, extendedData, attributeName, geometryNode;

    // Placemark id
    if (feature.fid != null) {
        placemarkNode.setAttribute("id", feature.fid);
    }

    // Placemark name
    name = feature.style && feature.style.label ? feature.style.label : feature.attributes.name || feature.id;
    placemarkName.appendChild(this.createTextNode(name));
    placemarkNode.appendChild(placemarkName);

    // Placemark description
    desc = feature.attributes.description || this.placemarksDesc;
    placemarkDesc.appendChild(this.createTextNode(desc));
    placemarkNode.appendChild(placemarkDesc);

    // Geometry node (Point, LineString, etc. nodes)
    geometryNode = this.buildGeometryNode(feature.geometry);
    placemarkNode.appendChild(geometryNode);

    // Search for extended data (see KML spec).
    for (attributeName in feature.attributes) {
        if (feature.attributes[attributeName].value) {
            if (!extendedData) {
                extendedData = this.createElementNS(this.kmlns, "ExtendedData");
            }

            // value element is necessary
            var data = this.createElementNS(this.kmlns, "Data"),
                value = this.createElementNS(this.kmlns, "value");
            data.setAttribute("name", attributeName);
            value.appendChild(this.createTextNode(feature.attributes[attributeName].value));
            data.appendChild(value);
            extendedData.appendChild(data);

            // displayName element
            if (feature.attributes[attributeName].displayName) {
                var displayName = this.createElementNS(this.kmlns, "displayName");
                displayName.appendChild(this.createTextNode(feature.attributes[attributeName].displayName));
                data.appendChild(displayName);
                extendedData.appendChild(displayName);
            }
        }
    }
    if (extendedData) {
        placemarkNode.appendChild(extendedData);
    }

    // TODO: implement serialization for other placemark elements.
    // See KML spec http://code.google.com/apis/kml/documentation/kmlreference.html#placemark
    return placemarkNode;
}

[probins]

this raises another issue: what form should attributes take? At the moment, kml is the only format (I think) which creates attributes as objects; all the others are simple key=value pairs. This means that attributes read in from kml aren't compatible with those created from other formats. I assume that this was done to cater for displayName on Data extended data nodes (SimpleData doesn't have this). Your function above won't output anything for attributes in the normal key=value form. (You can test in examples/vector-formats.html)

As displayName is optional anyway and won't be present on many if not most extendedData, I would question whether this incompatibility is worth it, and whether it wouldn't be better to store both Data and SimpleData nodes as simple key=value pairs, the same as other formats.