code: def get_field_names(self):
          
          col_model = self.request.get("colModel", None)
          if not col_model:
              return ["UID",]
  
          names = []
          col_model = json.loads(_u(col_model))
          if isinstance(col_model, (list, tuple)):
              names = map(lambda c: c.get("columnName", "").strip(), col_model)
  
          # UID is used by reference widget to know the object that the user
          # selected from the popup list
          if "UID" not in names:
              names.append("UID")
  
          return filter(None, names)
docs: Return the field names to get values for