Data Services - REST-ful URLs and path substitution parameters

Question

It is common for REST-full APIs (implemented on top of HTTPService) to require URL paths to contain substitution parameters.  For example, if my service end point is defined as 'http://...../rest/users/{id}/workspaces', then it would be nice if the generated service wrapper included a parameter for the substitution values - ie "function get_userWorkspaces(id:String) : AsyncToken "

Answer 1

I found a technique to achieve this using a custom Serializer for the Service Operation that overrides the "serializeURL" method.  However due to a bug (see SDK-21872 ) the technique doesnt work in FB4 beta 1.  See code snippet below...         
package services.listeningpost
import com.adobe.serializers.xml.XMLSerializationFilter;
import mx.rpc.http.Operation;
public class ListeningPost extends _Super_ListeningPost
protected var pathParams:Object = [];
public function setPathParam(key:String, value:String):void
pathParams[key] = value;
public function getPathParam(key:String):String
return pathParams[key];
private var _serializer:LPXMLSerializationFilter;
public function ListeningPost()
    _serializer = new LPXMLSerializationFilter(this);
    super;
    for each(var o:Operation in this.operations){
    if (o.serializationFilter is XMLSerializationFilter)
    o.serializationFilter = _serializer;
// Private class below provides custom Serializer
import com.adobe.serializers.xml.XMLSerializationFilter;
import mx.rpc.http.AbstractOperation;
import services.listeningpost.ListeningPost;
class LPXMLSerializationFilter extends XMLSerializationFilter{
private var _service:ListeningPost;
public function LPXMLSerializationFilter(service:ListeningPost)
super();
_service = service;
override public function serializeURL(operation:AbstractOperation, obj:Object, url:String) : String
var useUrl:String = super.serializeURL(operation,obj,url);
var keys:Array = useUrl.match(/\{([^\}]*)\}/g);
for each(var s:String in keys){
var r:String = _service.getPathParam(s);
if (r != null)
useUrl = useUrl.replace(s,r);
return useUrl;