def dumps(self, obj, many=None, *args, **kwargs):
        """Same as :meth:`dump`, except return a JSON-encoded string.

        :param obj: The object to serialize.
        :param bool many: Whether to serialize `obj` as a collection. If `None`, the value
            for `self.many` is used.
        :return: A ``json`` string
        :rtype: str

        .. versionadded:: 1.0.0
        .. versionchanged:: 3.0.0b7
            This method returns the serialized data rather than a ``(data, errors)`` duple.
            A :exc:`ValidationError <marshmallow.exceptions.ValidationError>` is raised
            if ``obj`` is invalid.
        """
        serialized = self.dump(obj, many=many)
        return self.opts.render_module.dumps(serialized, *args, **kwargs)