code: def _get_fields(cls, cols):
          
          return [sqla.literal_column(c.get('name')).label(c.get('name').replace('.', '__'))
                  for c in cols]
docs: BigQuery dialect requires us to not use backtick in the fieldname which are
          nested.
          Using literal_column handles that issue.
          https://docs.sqlalchemy.org/en/latest/core/tutorial.html#using-more-specific-text-with-table-literal-column-and-column
          Also explicility specifying column names so we don't encounter duplicate
          column names in the result.