def existing_node_check(self):
        qset = smart_fqdn_exists(self.fqdn, cn=False)
        if qset:
            objects = qset.all()
            raise ValidationError("Objects with this name already exist: {0}".
                                  format(objects))
        MX = mozdns.mx.models.MX
        if MX.objects.filter(server=self.fqdn):
            raise ValidationError("RFC 2181 says you shouldn't point MX "
                                  "records at CNAMEs and an MX points to"
                                  " this name!")
        # There are preexisting records that break this rule. We can't support
        # this requirement until those records are fixed
        # PTR = mozdns.ptr.models.PTR
        # if PTR.objects.filter(name=self.fqdn):
        #    raise ValidationError("RFC 1034 says you shouldn't point PTR "
        #                          "records at CNAMEs, and a PTR points to"
        #                          " this name!")

        # Should SRV's not be allowed to point to a CNAME? /me looks for an RFC
Takes a `glance_store.location.Location` object that indicates
dataset/ETHPy150Open rtucker-mozilla/mozilla_inventory/mozdns/cname/models.py/CNAME.existing_node_check--crossover with--dataset/ETHPy150Open openstack/glance_store/glance_store/_drivers/s3.py/Store.delete