Set the where clause for the relation query.

        :return: self
        :rtype: BelongsToMany

def _set_where(self):
        """
        Set the where clause for the relation query.

        :return: self
        :rtype: BelongsToMany
        """
        super(MorphToMany, self)._set_where()

        self._query.where("%s.%s" % (self._table, self._morph_type), self._morph_name)