gistfile1.txt

def to_json(self, view='list_view'):
  out = {}

  for f in self.get_fields(view):
      field_value = getattr(self, f)

      if hasattr(f, 'to_json'):              
          out[f] = field_value.to_json(view) # relation object
      elif hasattr(f, 'isoformat'):        
          out[f] = field_value.isoformat()   # datetime object
      else:
          out[f] = field_value

      return out

This is a method in the base class that all the models inherit from. Can't work out why the to_json method isn't found when it encounters a model object.