def isValidIDList(self, field_data, all_data):
        mod = self.rel.to
        try:
            pks = map(int, field_data.split(','))
        except ValueError:
            # the CommaSeparatedIntegerField validator will catch this error
            return
        objects = mod._default_manager.in_bulk(pks)
        if len(objects) != len(pks):
            badkeys = [k for k in pks if k not in objects]
            raise validators.ValidationError, ngettext("Please enter valid %(self)s IDs. The value %(value)r is invalid.",
                    "Please enter valid %(self)s IDs. The values %(value)r are invalid.", len(badkeys)) % {
                'self': self.verbose_name,
                'value': len(badkeys) == 1 and badkeys[0] or tuple(badkeys),
            }
Validates that the value is a valid list of foreign keys
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-0.96/django/db/models/fields/related.py/ManyToManyField.isValidIDList