How to specify success function for loader

[zolotoy]

I am trying to adapt the following example:
http://jsfiddle.net/dvAcu/

My goal is to load data when a node is expanded. How would I return data back to loader's success function if I am getting data into a callback?
I wrote something like this for testing:

Code:

loader:function(param,success,error){
                    if (!param.id)
                        promise = assetsMVCService.execute("assetprojectstatus", { assetId: 1, dataFormat: 'attribute' });
                    else
                        promise = assetsMVCService.execute("assetprojectstatus", { assetId: param.id, dataFormat: 'attribute' });
                    //promise.then(scope.assetChildren);
                    success(promise.then(scope.assetChildren)); // tried that, not working
                },

Initially data is loaded because param.id does not exist. When I click on a node I am getting into scope.assetChildren function but returning data from it is not working.
I dont see it and the node that's been expanded stays closed.

Please share some ideas.

Thanks