docs: def charge_documents(self):
      """
      This method allow you to charge documents you already have
          in your database. In this way an Index would be created according to
          the model and fields registered.
      """
  
      doc_count   = self._whoosh.doc_count()
      objs        = orm.count(e for e in self._model)
  
      field_names = set(self._schema_attrs.keys())
      missings    = set(self._whoosh.schema.names())
  
      for f in list(field_names - missings):
          self.add_field(f, fields.TEXT(self.kw))
  
      if doc_count == 0 and objs > 0:
        writer = self._whoosh.writer()
        for obj in orm.select(e for e in self._model):
          attrs = {self._primary_key: obj.get_pk()}
          for f in list(self._schema_attrs.keys()):
            attrs[f] = str(getattr(obj, f))
          writer.add_document(**attrs)
        writer.commit()