How to use the jardin.database.DatabaseAdapter function in jardin

def query_schema(self):
        db_adapter = DatabaseAdapter(
            self.db(role='replica', db_name=self.db_names.get('replica')),
            self.model_metadata(include_schema=False)
            )
        return db_adapter.raw_query(
            sql=db_adapter.db.lexicon.table_schema_query(self._table_name()),
            where={'table_name': self._table_name()}
            ).to_dict(orient='records')

def db_adapter(self, role='replica', db_name=None):
        if not hasattr(self, '_db_metadata'):
            self._db_metadata = {}
        db_name = db_name or self.db_names.get(role)
        key = '%s_%s' % (db_name, role)
        if key not in self._db_metadata:
            self._db_metadata[key] = self.model_metadata()
        return DatabaseAdapter(
            self.db(role=role, db_name=db_name),
            self._db_metadata[key]
            )