A service for managing and provisioning Bare Metal servers.
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ironic/ironic/db/sqlalchemy/api.py

843 lines
31 KiB

# -*- encoding: utf-8 -*-
#
# Copyright 2013 Hewlett-Packard Development Company, L.P.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
"""SQLAlchemy storage backend."""
import collections
import datetime
import threading
from oslo_config import cfg
from oslo_db import exception as db_exc
from oslo_db.sqlalchemy import enginefacade
from oslo_db.sqlalchemy import utils as db_utils
from oslo_log import log
from oslo_utils import strutils
from oslo_utils import timeutils
from oslo_utils import uuidutils
from sqlalchemy.orm.exc import NoResultFound
from sqlalchemy.orm import joinedload
from sqlalchemy import sql
from ironic.common import exception
from ironic.common.i18n import _
from ironic.common.i18n import _LW
from ironic.common import states
from ironic.common import utils
from ironic.db import api
from ironic.db.sqlalchemy import models
CONF = cfg.CONF
CONF.import_opt('heartbeat_timeout',
'ironic.conductor.manager',
group='conductor')
LOG = log.getLogger(__name__)
_CONTEXT = threading.local()
def get_backend():
"""The backend is this module itself."""
return Connection()
def _session_for_read():
return enginefacade.reader.using(_CONTEXT)
def _session_for_write():
return enginefacade.writer.using(_CONTEXT)
def _get_node_query_with_tags():
return model_query(models.Node).options(joinedload('tags'))
def model_query(model, *args, **kwargs):
"""Query helper for simpler session usage.
:param session: if present, the session to use
"""
with _session_for_read() as session:
query = session.query(model, *args)
return query
def add_identity_filter(query, value):
"""Adds an identity filter to a query.
Filters results by ID, if supplied value is a valid integer.
Otherwise attempts to filter results by UUID.
:param query: Initial query to add filter to.
:param value: Value for filtering results by.
:return: Modified query.
"""
if strutils.is_int_like(value):
return query.filter_by(id=value)
elif uuidutils.is_uuid_like(value):
return query.filter_by(uuid=value)
else:
raise exception.InvalidIdentity(identity=value)
def add_port_filter(query, value):
"""Adds a port-specific filter to a query.
Filters results by address, if supplied value is a valid MAC
address. Otherwise attempts to filter results by identity.
:param query: Initial query to add filter to.
:param value: Value for filtering results by.
:return: Modified query.
"""
if utils.is_valid_mac(value):
return query.filter_by(address=value)
else:
return add_identity_filter(query, value)
def add_port_filter_by_node(query, value):
if strutils.is_int_like(value):
return query.filter_by(node_id=value)
else:
query = query.join(models.Node,
models.Port.node_id == models.Node.id)
return query.filter(models.Node.uuid == value)
def add_portgroup_filter(query, value):
"""Adds a portgroup-specific filter to a query.
Filters results by address, if supplied value is a valid MAC
address. Otherwise attempts to filter results by identity.
:param query: Initial query to add filter to.
:param value: Value for filtering results by.
:return: Modified query.
"""
if utils.is_valid_mac(value):
return query.filter_by(address=value)
else:
return add_identity_filter(query, value)
def add_portgroup_filter_by_node(query, value):
if strutils.is_int_like(value):
return query.filter_by(node_id=value)
else:
query = query.join(models.Node,
models.Portgroup.node_id == models.Node.id)
return query.filter(models.Node.uuid == value)
def add_port_filter_by_portgroup(query, value):
if strutils.is_int_like(value):
return query.filter_by(portgroup_id=value)
else:
query = query.join(models.Portgroup,
models.Port.portgroup_id == models.Portgroup.id)
return query.filter(models.Portgroup.uuid == value)
def add_node_filter_by_chassis(query, value):
if strutils.is_int_like(value):
return query.filter_by(chassis_id=value)
else:
query = query.join(models.Chassis,
models.Node.chassis_id == models.Chassis.id)
return query.filter(models.Chassis.uuid == value)
def _paginate_query(model, limit=None, marker=None, sort_key=None,
sort_dir=None, query=None):
if not query:
query = model_query(model)
sort_keys = ['id']
if sort_key and sort_key not in sort_keys:
sort_keys.insert(0, sort_key)
try:
query = db_utils.paginate_query(query, model, limit, sort_keys,
marker=marker, sort_dir=sort_dir)
except db_exc.InvalidSortKey:
raise exception.InvalidParameterValue(
_('The sort_key value "%(key)s" is an invalid field for sorting')
% {'key': sort_key})
return query.all()
class Connection(api.Connection):
"""SqlAlchemy connection."""
def __init__(self):
pass
def _add_nodes_filters(self, query, filters):
if filters is None:
filters = []
if 'chassis_uuid' in filters:
# get_chassis_by_uuid() to raise an exception if the chassis
# is not found
chassis_obj = self.get_chassis_by_uuid(filters['chassis_uuid'])
query = query.filter_by(chassis_id=chassis_obj.id)
if 'associated' in filters:
if filters['associated']:
query = query.filter(models.Node.instance_uuid != sql.null())
else:
query = query.filter(models.Node.instance_uuid == sql.null())
if 'reserved' in filters:
if filters['reserved']:
query = query.filter(models.Node.reservation != sql.null())
else:
query = query.filter(models.Node.reservation == sql.null())
if 'reserved_by_any_of' in filters:
query = query.filter(models.Node.reservation.in_(
filters['reserved_by_any_of']))
if 'maintenance' in filters:
query = query.filter_by(maintenance=filters['maintenance'])
if 'driver' in filters:
query = query.filter_by(driver=filters['driver'])
if 'provision_state' in filters:
query = query.filter_by(provision_state=filters['provision_state'])
if 'provisioned_before' in filters:
limit = (timeutils.utcnow() -
datetime.timedelta(seconds=filters['provisioned_before']))
query = query.filter(models.Node.provision_updated_at < limit)
if 'inspection_started_before' in filters:
limit = ((timeutils.utcnow()) -
(datetime.timedelta(
seconds=filters['inspection_started_before'])))
query = query.filter(models.Node.inspection_started_at < limit)
return query
def get_nodeinfo_list(self, columns=None, filters=None, limit=None,
marker=None, sort_key=None, sort_dir=None):
# list-ify columns default values because it is bad form
# to include a mutable list in function definitions.
if columns is None:
columns = [models.Node.id]
else:
columns = [getattr(models.Node, c) for c in columns]
query = model_query(*columns, base_model=models.Node)
query = self._add_nodes_filters(query, filters)
return _paginate_query(models.Node, limit, marker,
sort_key, sort_dir, query)
def get_node_list(self, filters=None, limit=None, marker=None,
sort_key=None, sort_dir=None):
query = _get_node_query_with_tags()
query = self._add_nodes_filters(query, filters)
return _paginate_query(models.Node, limit, marker,
sort_key, sort_dir, query)
def reserve_node(self, tag, node_id):
with _session_for_write():
query = _get_node_query_with_tags()
query = add_identity_filter(query, node_id)
# be optimistic and assume we usually create a reservation
count = query.filter_by(reservation=None).update(
{'reservation': tag}, synchronize_session=False)
try:
node = query.one()
if count != 1:
# Nothing updated and node exists. Must already be
# locked.
raise exception.NodeLocked(node=node.uuid,
host=node['reservation'])
return node
except NoResultFound:
raise exception.NodeNotFound(node_id)
def release_node(self, tag, node_id):
with _session_for_write():
query = model_query(models.Node)
query = add_identity_filter(query, node_id)
# be optimistic and assume we usually release a reservation
count = query.filter_by(reservation=tag).update(
{'reservation': None}, synchronize_session=False)
try:
if count != 1:
node = query.one()
if node['reservation'] is None:
raise exception.NodeNotLocked(node=node.uuid)
else:
raise exception.NodeLocked(node=node.uuid,
host=node['reservation'])
except NoResultFound:
raise exception.NodeNotFound(node_id)
def create_node(self, values):
# ensure defaults are present for new nodes
if 'uuid' not in values:
values['uuid'] = uuidutils.generate_uuid()
if 'power_state' not in values:
values['power_state'] = states.NOSTATE
if 'provision_state' not in values:
values['provision_state'] = states.ENROLL
# TODO(zhenguo): Support creating node with tags
if 'tags' in values:
LOG.warning(
_LW('Ignore the specified tags %(tags)s when creating node: '
'%(node)s.'), {'tags': values['tags'],
'node': values['uuid']})
del values['tags']
node = models.Node()
node.update(values)
with _session_for_write() as session:
try:
session.add(node)
session.flush()
except db_exc.DBDuplicateEntry as exc:
if 'name' in exc.columns:
raise exception.DuplicateName(name=values['name'])
elif 'instance_uuid' in exc.columns:
raise exception.InstanceAssociated(
instance_uuid=values['instance_uuid'],
node=values['uuid'])
raise exception.NodeAlreadyExists(uuid=values['uuid'])
# Set tags to [] for new created node
node['tags'] = []
return node
def get_node_by_id(self, node_id):
query = _get_node_query_with_tags()
query = query.filter_by(id=node_id)
try:
return query.one()
except NoResultFound:
raise exception.NodeNotFound(node=node_id)
def get_node_by_uuid(self, node_uuid):
query = _get_node_query_with_tags()
query = query.filter_by(uuid=node_uuid)
try:
return query.one()
except NoResultFound:
raise exception.NodeNotFound(node=node_uuid)
def get_node_by_name(self, node_name):
query = _get_node_query_with_tags()
query = query.filter_by(name=node_name)
try:
return query.one()
except NoResultFound:
raise exception.NodeNotFound(node=node_name)
def get_node_by_instance(self, instance):
if not uuidutils.is_uuid_like(instance):
raise exception.InvalidUUID(uuid=instance)
query = _get_node_query_with_tags()
query = query.filter_by(instance_uuid=instance)
try:
result = query.one()
except NoResultFound:
raise exception.InstanceNotFound(instance=instance)
return result
def destroy_node(self, node_id):
with _session_for_write():
query = model_query(models.Node)
query = add_identity_filter(query, node_id)
try:
node_ref = query.one()
except NoResultFound:
raise exception.NodeNotFound(node=node_id)
# Get node ID, if an UUID was supplied. The ID is
# required for deleting all ports, attached to the node.
if uuidutils.is_uuid_like(node_id):
node_id = node_ref['id']
port_query = model_query(models.Port)
port_query = add_port_filter_by_node(port_query, node_id)
port_query.delete()
portgroup_query = model_query(models.Portgroup)
portgroup_query = add_portgroup_filter_by_node(portgroup_query,
node_id)
portgroup_query.delete()
# Delete all tags attached to the node
tag_query = model_query(models.NodeTag).filter_by(node_id=node_id)
tag_query.delete()
query.delete()
def update_node(self, node_id, values):
# NOTE(dtantsur): this can lead to very strange errors
if 'uuid' in values:
msg = _("Cannot overwrite UUID for an existing Node.")
raise exception.InvalidParameterValue(err=msg)
try:
return self._do_update_node(node_id, values)
except db_exc.DBDuplicateEntry as e:
if 'name' in e.columns:
raise exception.DuplicateName(name=values['name'])
elif 'uuid' in e.columns:
raise exception.NodeAlreadyExists(uuid=values['uuid'])
elif 'instance_uuid' in e.columns:
raise exception.InstanceAssociated(
instance_uuid=values['instance_uuid'],
node=node_id)
else:
raise e
def _do_update_node(self, node_id, values):
with _session_for_write():
query = model_query(models.Node)
query = add_identity_filter(query, node_id)
try:
ref = query.with_lockmode('update').one()
except NoResultFound:
raise exception.NodeNotFound(node=node_id)
# Prevent instance_uuid overwriting
if values.get("instance_uuid") and ref.instance_uuid:
raise exception.NodeAssociated(
node=ref.uuid, instance=ref.instance_uuid)
if 'provision_state' in values:
values['provision_updated_at'] = timeutils.utcnow()
if values['provision_state'] == states.INSPECTING:
values['inspection_started_at'] = timeutils.utcnow()
values['inspection_finished_at'] = None
elif (ref.provision_state == states.INSPECTING and
values['provision_state'] == states.MANAGEABLE):
values['inspection_finished_at'] = timeutils.utcnow()
values['inspection_started_at'] = None
elif (ref.provision_state == states.INSPECTING and
values['provision_state'] == states.INSPECTFAIL):
values['inspection_started_at'] = None
ref.update(values)
return ref
def get_port_by_id(self, port_id):
query = model_query(models.Port).filter_by(id=port_id)
try:
return query.one()
except NoResultFound:
raise exception.PortNotFound(port=port_id)
def get_port_by_uuid(self, port_uuid):
query = model_query(models.Port).filter_by(uuid=port_uuid)
try:
return query.one()
except NoResultFound:
raise exception.PortNotFound(port=port_uuid)
def get_port_by_address(self, address):
query = model_query(models.Port).filter_by(address=address)
try:
return query.one()
except NoResultFound:
raise exception.PortNotFound(port=address)
def get_port_list(self, limit=None, marker=None,
sort_key=None, sort_dir=None):
return _paginate_query(models.Port, limit, marker,
sort_key, sort_dir)
def get_ports_by_node_id(self, node_id, limit=None, marker=None,
sort_key=None, sort_dir=None):
query = model_query(models.Port)
query = query.filter_by(node_id=node_id)
return _paginate_query(models.Port, limit, marker,
sort_key, sort_dir, query)
def get_ports_by_portgroup_id(self, portgroup_id, limit=None, marker=None,
sort_key=None, sort_dir=None):
query = model_query(models.Port)
query = query.filter_by(portgroup_id=portgroup_id)
return _paginate_query(models.Port, limit, marker,
sort_key, sort_dir, query)
def create_port(self, values):
if not values.get('uuid'):
values['uuid'] = uuidutils.generate_uuid()
port = models.Port()
port.update(values)
with _session_for_write() as session:
try:
session.add(port)
session.flush()
except db_exc.DBDuplicateEntry as exc:
if 'address' in exc.columns:
raise exception.MACAlreadyExists(mac=values['address'])
raise exception.PortAlreadyExists(uuid=values['uuid'])
return port
def update_port(self, port_id, values):
# NOTE(dtantsur): this can lead to very strange errors
if 'uuid' in values:
msg = _("Cannot overwrite UUID for an existing Port.")
raise exception.InvalidParameterValue(err=msg)
try:
with _session_for_write() as session:
query = model_query(models.Port)
query = add_port_filter(query, port_id)
ref = query.one()
ref.update(values)
session.flush()
except NoResultFound:
raise exception.PortNotFound(port=port_id)
except db_exc.DBDuplicateEntry:
raise exception.MACAlreadyExists(mac=values['address'])
return ref
def destroy_port(self, port_id):
with _session_for_write():
query = model_query(models.Port)
query = add_port_filter(query, port_id)
count = query.delete()
if count == 0:
raise exception.PortNotFound(port=port_id)
def get_portgroup_by_id(self, portgroup_id):
query = model_query(models.Portgroup).filter_by(id=portgroup_id)
try:
return query.one()
except NoResultFound:
raise exception.PortgroupNotFound(portgroup=portgroup_id)
def get_portgroup_by_uuid(self, portgroup_uuid):
query = model_query(models.Portgroup).filter_by(uuid=portgroup_uuid)
try:
return query.one()
except NoResultFound:
raise exception.PortgroupNotFound(portgroup=portgroup_uuid)
def get_portgroup_by_address(self, address):
query = model_query(models.Portgroup).filter_by(address=address)
try:
return query.one()
except NoResultFound:
raise exception.PortgroupNotFound(portgroup=address)
def get_portgroup_by_name(self, name):
query = model_query(models.Portgroup).filter_by(name=name)
try:
return query.one()
except NoResultFound:
raise exception.PortgroupNotFound(portgroup=name)
def get_portgroup_list(self, limit=None, marker=None,
sort_key=None, sort_dir=None):
return _paginate_query(models.Portgroup, limit, marker,
sort_key, sort_dir)
def get_portgroups_by_node_id(self, node_id, limit=None, marker=None,
sort_key=None, sort_dir=None):
query = model_query(models.Portgroup)
query = query.filter_by(node_id=node_id)
return _paginate_query(models.Portgroup, limit, marker,
sort_key, sort_dir, query)
def create_portgroup(self, values):
if not values.get('uuid'):
values['uuid'] = uuidutils.generate_uuid()
portgroup = models.Portgroup()
portgroup.update(values)
with _session_for_write() as session:
try:
session.add(portgroup)
session.flush()
except db_exc.DBDuplicateEntry as exc:
if 'name' in exc.columns:
raise exception.PortgroupDuplicateName(name=values['name'])
elif 'address' in exc.columns:
raise exception.PortgroupMACAlreadyExists(
mac=values['address'])
raise exception.PortgroupAlreadyExists(uuid=values['uuid'])
return portgroup
def update_portgroup(self, portgroup_id, values):
if 'uuid' in values:
msg = _("Cannot overwrite UUID for an existing portgroup.")
raise exception.InvalidParameterValue(err=msg)
with _session_for_write() as session:
try:
query = model_query(models.Portgroup)
query = add_portgroup_filter(query, portgroup_id)
ref = query.one()
ref.update(values)
session.flush()
except NoResultFound:
raise exception.PortgroupNotFound(portgroup=portgroup_id)
except db_exc.DBDuplicateEntry as exc:
if 'name' in exc.columns:
raise exception.PortgroupDuplicateName(name=values['name'])
elif 'address' in exc.columns:
raise exception.PortgroupMACAlreadyExists(
mac=values['address'])
else:
raise exc
return ref
def destroy_portgroup(self, portgroup_id):
def portgroup_not_empty(session):
"""Checks whether the portgroup does not have ports."""
query = model_query(models.Port)
query = add_port_filter_by_portgroup(query, portgroup_id)
return query.count() != 0
with _session_for_write() as session:
if portgroup_not_empty(session):
raise exception.PortgroupNotEmpty(portgroup=portgroup_id)
query = model_query(models.Portgroup, session=session)
query = add_identity_filter(query, portgroup_id)
count = query.delete()
if count == 0:
raise exception.PortgroupNotFound(portgroup=portgroup_id)
def get_chassis_by_id(self, chassis_id):
query = model_query(models.Chassis).filter_by(id=chassis_id)
try:
return query.one()
except NoResultFound:
raise exception.ChassisNotFound(chassis=chassis_id)
def get_chassis_by_uuid(self, chassis_uuid):
query = model_query(models.Chassis).filter_by(uuid=chassis_uuid)
try:
return query.one()
except NoResultFound:
raise exception.ChassisNotFound(chassis=chassis_uuid)
def get_chassis_list(self, limit=None, marker=None,
sort_key=None, sort_dir=None):
return _paginate_query(models.Chassis, limit, marker,
sort_key, sort_dir)
def create_chassis(self, values):
if not values.get('uuid'):
values['uuid'] = uuidutils.generate_uuid()
chassis = models.Chassis()
chassis.update(values)
with _session_for_write() as session:
try:
session.add(chassis)
session.flush()
except db_exc.DBDuplicateEntry:
raise exception.ChassisAlreadyExists(uuid=values['uuid'])
return chassis
def update_chassis(self, chassis_id, values):
# NOTE(dtantsur): this can lead to very strange errors
if 'uuid' in values:
msg = _("Cannot overwrite UUID for an existing Chassis.")
raise exception.InvalidParameterValue(err=msg)
with _session_for_write():
query = model_query(models.Chassis)
query = add_identity_filter(query, chassis_id)
count = query.update(values)
if count != 1:
raise exception.ChassisNotFound(chassis=chassis_id)
ref = query.one()
return ref
def destroy_chassis(self, chassis_id):
def chassis_not_empty():
"""Checks whether the chassis does not have nodes."""
query = model_query(models.Node)
query = add_node_filter_by_chassis(query, chassis_id)
return query.count() != 0
with _session_for_write():
if chassis_not_empty():
raise exception.ChassisNotEmpty(chassis=chassis_id)
query = model_query(models.Chassis)
query = add_identity_filter(query, chassis_id)
count = query.delete()
if count != 1:
raise exception.ChassisNotFound(chassis=chassis_id)
def register_conductor(self, values, update_existing=False):
with _session_for_write() as session:
query = (model_query(models.Conductor)
.filter_by(hostname=values['hostname']))
try:
ref = query.one()
if ref.online is True and not update_existing:
raise exception.ConductorAlreadyRegistered(
conductor=values['hostname'])
except NoResultFound:
ref = models.Conductor()
session.add(ref)
ref.update(values)
# always set online and updated_at fields when registering
# a conductor, especially when updating an existing one
ref.update({'updated_at': timeutils.utcnow(),
'online': True})
return ref
def get_conductor(self, hostname):
try:
return (model_query(models.Conductor)
.filter_by(hostname=hostname, online=True)
.one())
except NoResultFound:
raise exception.ConductorNotFound(conductor=hostname)
def unregister_conductor(self, hostname):
with _session_for_write():
query = (model_query(models.Conductor)
.filter_by(hostname=hostname, online=True))
count = query.update({'online': False})
if count == 0:
raise exception.ConductorNotFound(conductor=hostname)
def touch_conductor(self, hostname):
with _session_for_write():
query = (model_query(models.Conductor)
.filter_by(hostname=hostname))
# since we're not changing any other field, manually set updated_at
# and since we're heartbeating, make sure that online=True
count = query.update({'updated_at': timeutils.utcnow(),
'online': True})
if count == 0:
raise exception.ConductorNotFound(conductor=hostname)
def clear_node_reservations_for_conductor(self, hostname):
nodes = []
with _session_for_write():
query = (model_query(models.Node)
.filter_by(reservation=hostname))
nodes = [node['uuid'] for node in query]
query.update({'reservation': None})
if nodes:
nodes = ', '.join(nodes)
LOG.warning(
_LW('Cleared reservations held by %(hostname)s: '
'%(nodes)s'), {'hostname': hostname, 'nodes': nodes})
def get_active_driver_dict(self, interval=None):
if interval is None:
interval = CONF.conductor.heartbeat_timeout
limit = timeutils.utcnow() - datetime.timedelta(seconds=interval)
result = (model_query(models.Conductor)
.filter_by(online=True)
.filter(models.Conductor.updated_at >= limit)
.all())
# build mapping of drivers to the set of hosts which support them
d2c = collections.defaultdict(set)
for row in result:
for driver in row['drivers']:
d2c[driver].add(row['hostname'])
return d2c
def get_offline_conductors(self):
interval = CONF.conductor.heartbeat_timeout
limit = timeutils.utcnow() - datetime.timedelta(seconds=interval)
result = (model_query(models.Conductor).filter_by()
.filter(models.Conductor.updated_at < limit)
.all())
return [row['hostname'] for row in result]
def touch_node_provisioning(self, node_id):
with _session_for_write():
query = model_query(models.Node)
query = add_identity_filter(query, node_id)
count = query.update({'provision_updated_at': timeutils.utcnow()})
if count == 0:
raise exception.NodeNotFound(node_id)
def _check_node_exists(self, node_id):
if not model_query(models.Node).filter_by(id=node_id).scalar():
raise exception.NodeNotFound(node=node_id)
def set_node_tags(self, node_id, tags):
# remove duplicate tags
tags = set(tags)
with _session_for_write() as session:
self.unset_node_tags(node_id)
node_tags = []
for tag in tags:
node_tag = models.NodeTag(tag=tag, node_id=node_id)
session.add(node_tag)
node_tags.append(node_tag)
return node_tags
def unset_node_tags(self, node_id):
self._check_node_exists(node_id)
with _session_for_write():
model_query(models.NodeTag).filter_by(node_id=node_id).delete()
def get_node_tags_by_node_id(self, node_id):
self._check_node_exists(node_id)
result = (model_query(models.NodeTag)
.filter_by(node_id=node_id)
.all())
return result
def add_node_tag(self, node_id, tag):
node_tag = models.NodeTag(tag=tag, node_id=node_id)
self._check_node_exists(node_id)
try:
with _session_for_write() as session:
session.add(node_tag)
session.flush()
except db_exc.DBDuplicateEntry:
# NOTE(zhenguo): ignore tags duplicates
pass
return node_tag
def delete_node_tag(self, node_id, tag):
self._check_node_exists(node_id)
with _session_for_write():
result = model_query(models.NodeTag).filter_by(
node_id=node_id, tag=tag).delete()
if not result:
raise exception.NodeTagNotFound(node_id=node_id, tag=tag)
def node_tag_exists(self, node_id, tag):
q = model_query(models.NodeTag).filter_by(node_id=node_id, tag=tag)
return model_query(q.exists()).scalar()