Create a "where" query with this collection as parent.

        See
        :meth:`~.firestore_v1beta1.query.Query.where` for
        more information on this method.

        Args:
            field_path (str): A field path (``.``-delimited list of
                field names) for the field to filter on.
            op_string (str): A comparison operation in the form of a string.
                Acceptable values are ``<``, ``<=``, ``==``, ``>=``
                and ``>``.
            value (Any): The value to compare the field against in the filter.
                If ``value`` is :data:`None` or a NaN, then ``==`` is the only
                allowed operation.

        Returns:
            ~.firestore_v1beta1.query.Query: A filtered query.

def where(self, field_path, op_string, value):
        """Create a "where" query with this collection as parent.

        See
        :meth:`~.firestore_v1beta1.query.Query.where` for
        more information on this method.

        Args:
            field_path (str): A field path (``.``-delimited list of
                field names) for the field to filter on.
            op_string (str): A comparison operation in the form of a string.
                Acceptable values are ``<``, ``<=``, ``==``, ``>=``
                and ``>``.
            value (Any): The value to compare the field against in the filter.
                If ``value`` is :data:`None` or a NaN, then ``==`` is the only
                allowed operation.

        Returns:
            ~.firestore_v1beta1.query.Query: A filtered query.
        """
        query = query_mod.Query(self)
        return query.where(field_path, op_string, value)