PersistableObject.addListener

    public static void addListener(PropertyChangeSetListener listener) {
    	Map<ObjectId, Set<String>> readSet = readSets.get();
    	Map<ObjectId, Set<String>> watchSet = watchSets.get(listener);
    	if (watchSet == null){
    		synchronized(watchSets){
    			watchSets.put(listener,watchSet = new HashMap<ObjectId, Set<String>>());
    		}
    	}
		for (Map.Entry<ObjectId, Set<String>> entry : readSet.entrySet()) {
			ObjectId key = entry.getKey();
			Set<String> value = entry.getValue();
			if (watchSet.containsKey(key) && value != FullSet.instance)
				watchSet.get(key).addAll(value);
			else{
				if(watchSet.containsKey(key) && key instanceof Query && ((Query)key).conditionFunction != null){
			
					ObjectId oldQuery = null;
					// find the old query (and it's conditionFunction)
					for(Map.Entry<ObjectId, Set<String>> watchEntry : watchSet.entrySet()){
						oldQuery = watchEntry.getKey();
						if(oldQuery.equals(key)){
							break;
						}
					}
					final Function newFunction = ((Query)key).conditionFunction;
					final Function oldFunction = ((Query)oldQuery).conditionFunction;
					// create a new function that combines the other two
					((Query)key).conditionFunction = new BaseFunction(){
						@Override
						public Object call(Context cx, Scriptable scope, Scriptable thisObj, Object[] args) {
							return ScriptRuntime.toBoolean(newFunction.call(cx, scope, thisObj, args)) ||
							ScriptRuntime.toBoolean(oldFunction.call(cx, scope, thisObj, args));
						}
					};
				}
				watchSet.put(key,value);
			}
		}
    }