docs: def filter(self, **kwargs):
      # @TODO refactor with models as dicts
      """filter results of dataset eg.
      
      Query('Posts').filter(post_type='post')
      """
      f_field = kwargs.keys()[0]
      f_value = kwargs[f_field]
      _newset = []
      
      for m in self._dataset:
        if hasattr(m, f_field):
          if getattr(m, f_field) == f_value:
            _newset.append(m)
      self._dataset = _newset
      return self