docs: def ins2dict(ins, kind=''):
      """Turn a SQLAlchemy Model instance to dict.
  
      :param ins: a SQLAlchemy instance.
      :param kind: specify which kind of dict tranformer should be called.
      :return: dict, instance data.
  
      If model has defined `to_xxx_dict`, then ins2dict(ins, 'xxx') will
      call `model.to_xxx_dict()`. Default kind is ''.
  
      If model not defined 'to_dict', then ins2dict will transform according
      by model column definition.
      """
      if kind and hasattr(ins, 'to_%s_dict' % kind):
          return getattr(ins, 'to_%s_dict' % kind)()
      elif hasattr(ins, 'to_dict'):
          return getattr(ins, 'to_dict')()
      else:
          return _turn_row_to_dict(ins)