Confusion with web server binding

[fatzopilot]

Hi,

It is probably only a tiny setting but I am banging my head around it for a while.
I am trying to set up a client side datasource to query a geolocation server.
Documentation on how to query it can be found here: http://open.mapquestapi.com/nominatim/

Since I thought it would be the most efficient to use JSON, I extended the XJSONDataSource and set

 
setDataFormat(DSDataFormat.JSON); //just to be sure
DSRequest dsr = new DSRequest();
dsr.setCallbackParam("json_callback"); //the server expects the callback method parameter to be like this
setRequestProperties(dsr);
setRecordXPath("//"); //setting it seems to make no difference
setDataURL("http://open.mapquestapi.com/nominatim/v1/search");

//Field definitions
DataSourceField osm_id = new DataSourceTextField("osm_id");
osm_id.setPrimaryKey(true);
osm_id.setHidden(true);
// AutoIncrement on server.
osm_id.setRequired(true);
addField(osm_id);

DataSourceField boundingbox = new DataSourceTextField("boundingbox");
boundingbox.setMultiple(true);
addField(boundingbox);

//a nested field
DataSourceTextField clazz = new DataSourceTextField("class");
clazz.setValueXPath("address");
addField(clazz);

DataSourceField licence = new DataSourceTextField("licence");
addField(licence);
...

The query string transmitted to the server (after setting the corresponding criteria) is then e.g.

http://open.mapquestapi.com/nominatim/v1/search?q=Manassas&format=json&json_callback=isc.Comm._scriptIncludeReply_1

Using Firebug, the response seems to turn out to be like an array that contains Maps, e.g.:

isc.Comm._scriptIncludeReply_1(
[  {
      "place_id":"504794",
      "licence":"Data Copyright OpenStreetMap Contributors, Some Rights Reserved. CC-BY-SA 2.0.",
      "osm_type":"node",
      "osm_id":"158544740",
      "boundingbox":[
         "38.7409460449",
         "38.7609498596",
         "-77.4852731323",
         "-77.4652655029"
      ],
      "lat":"38.7509488",
      "lon":"-77.4752667",
      "display_name":"Manassas, Manassas (city), Virginia, United States of America",
      "class":"place",
      "type":"town",
      "icon":"http://open.mapquestapi.com/nominatim/v1/images/mapicons/poi_place_town.p.20.png"
   },
   {
      "place_id":"79456270",
      "licence":"Data Copyright OpenStreetMap Contributors, Some Rights Reserved. CC-BY-SA 2.0.",
      "osm_type":"relation",
      "osm_id":"206870",
      "boundingbox":[
         "38.7079010009766",
         "38.7814140319824",
         "-77.5266799926758",
         "-77.447509765625"
      ],
      "lat":"38.7480051041384",
      "lon":"-77.4838009846557",
      "display_name":"Manassas, Prince William County, Virginia, United States of America",
      "class":"boundary",
      "type":"administrative",
      "icon":"http://open.mapquestapi.com/nominatim/v1/images/mapicons/poi_boundary_administrative.p.20.png"
   },
...])

The GWT DSCallback is called, response.getStatus() is 0, but response.getData().length is 0 as well. The develompment console indicates a successful call, so it must be a small binding issue. I searched the Quick Start Guide and the corresponding docs and studied the showcase examples but haven't found an example that works with json and callbacks.

What am I missing here?

Thanks
fatzopilot

[fatzopilot]

To be sure to not missing the obvious, could somebody come up with a simple example (at best, using a public server) that uses JSON as a message format and a json-callback?

Thanks
fatzopilot

[fatzopilot]

Setting
setRecordXPath("/");
instead of
setRecordXPath("//");
solves the problem.