'If any fields are marked to be deferred, returns a dictionary mapping
models to a set of names in those fields that will be loaded. If a
model is not in the returned dictionary, none of it\'s fields are
deferred.
If no fields are marked for deferral, returns an empty dictionary.'

def get_loaded_field_names(self):

    collection = {}
    self.deferred_to_data(collection, self.get_loaded_field_names_cb)
    return collection
