150 lines
6.0 KiB
Python
150 lines
6.0 KiB
Python
# Copyright 2011 VMware, Inc.
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# All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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import weakref
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from neutron_lib.db import api
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from neutron_lib.db import model_base
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import sqlalchemy
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from sqlalchemy import event # noqa
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from sqlalchemy import orm
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context_manager = api.get_context_manager()
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# Expire relationships when foreign key changes.
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#
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# NOTE(ihrachys) Arguably, it's a sqlalchemy anti-pattern to access child
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# models directly and through parent relationships in the same session. But
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# since OVO mechanism is built around synthetic fields that assume this mixed
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# access is possible, we keep it here until we find a way to migrate OVO
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# synthetic fields to better mechanism that would update child models via
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# parents. Even with that, there are multiple places in plugin code where we
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# mix access when using models directly; those occurrences would need to be
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# fixed too to be able to remove this hook and explicit expire() calls.
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#
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# Adopted from the following recipe:
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# https://bitbucket.org/zzzeek/sqlalchemy/wiki/UsageRecipes
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# /ExpireRelationshipOnFKChange
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#
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# ...then massively changed to actually work for all neutron backref cases.
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#
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# TODO(ihrachys) at some point these event handlers should be extended to also
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# automatically refresh values for expired attributes
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def _expire_for_fk_change(target, fk_value, relationship_prop, column_attr):
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"""Expire relationship attributes when a many-to-one column changes."""
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sess = orm.object_session(target)
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# subnets and network's many-to-one relationship is used as example in the
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# comments in this function
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if sess is not None:
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# optional behavior #1 - expire the "Network.subnets"
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# collection on the existing "network" object
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if relationship_prop.back_populates and \
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relationship_prop.key in target.__dict__:
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obj = getattr(target, relationship_prop.key)
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if obj is not None and sqlalchemy.inspect(obj).persistent:
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sess.expire(obj, [relationship_prop.back_populates])
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# optional behavior #2 - expire the "Subnet.network"
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if sqlalchemy.inspect(target).persistent:
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sess.expire(target, [relationship_prop.key])
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# optional behavior #3 - "trick" the ORM by actually
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# setting the value ahead of time, then emitting a load
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# for the attribute so that the *new* Subnet.network
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# is loaded. Then, expire Network.subnets on *that*.
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# Other techniques here including looking in the identity
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# map for "value", if this is a simple many-to-one get.
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if relationship_prop.back_populates:
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target.__dict__[column_attr] = fk_value
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new = getattr(target, relationship_prop.key)
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if new is not None:
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if sqlalchemy.inspect(new).persistent:
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sess.expire(new, [relationship_prop.back_populates])
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else:
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# no Session yet, do it later. This path is reached from the 'expire'
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# listener setup by '_expire_prop_on_col' below, when a foreign key
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# is directly assigned to in the many to one side of a relationship.
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# i.e. assigning directly to Subnet.network_id before Subnet is added
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# to the session
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if target not in _emit_on_pending:
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_emit_on_pending[target] = []
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_emit_on_pending[target].append(
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(fk_value, relationship_prop, column_attr))
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_emit_on_pending = weakref.WeakKeyDictionary()
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@event.listens_for(orm.session.Session, "pending_to_persistent")
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def _pending_callables(session, obj):
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"""Expire relationships when a new object w/ a foreign key becomes
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persistent
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"""
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if obj is None:
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return
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args = _emit_on_pending.pop(obj, [])
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for a in args:
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if a is not None:
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_expire_for_fk_change(obj, *a)
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@event.listens_for(orm.session.Session, "persistent_to_deleted")
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def _persistent_to_deleted(session, obj):
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"""Expire relationships when an object w/ a foreign key becomes deleted"""
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mapper = sqlalchemy.inspect(obj).mapper
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for prop in mapper.relationships:
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if prop.direction is orm.interfaces.MANYTOONE:
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for col in prop.local_columns:
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colkey = mapper.get_property_by_column(col).key
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_expire_for_fk_change(obj, None, prop, colkey)
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@event.listens_for(model_base.BASEV2, "attribute_instrument", propagate=True)
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def _listen_for_changes(cls, key, inst):
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mapper = sqlalchemy.inspect(cls)
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if key not in mapper.relationships:
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return
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prop = inst.property
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if prop.direction is orm.interfaces.MANYTOONE:
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for col in prop.local_columns:
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colkey = mapper.get_property_by_column(col).key
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_expire_prop_on_col(cls, prop, colkey)
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elif prop.direction is orm.interfaces.ONETOMANY:
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remote_mapper = prop.mapper
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# the collection *has* to have a MANYTOONE backref so we
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# can look up the parent. so here we make one if it doesn't
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# have it already, as is the case in this example
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if not prop.back_populates:
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name = "_%s_backref" % prop.key
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backref_prop = orm.relationship(
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prop.parent, back_populates=prop.key)
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remote_mapper.add_property(name, backref_prop)
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prop.back_populates = name
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def _expire_prop_on_col(cls, prop, colkey):
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@event.listens_for(getattr(cls, colkey), "set")
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def expire(target, value, oldvalue, initiator):
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"""Expire relationships when the foreign key attribute on
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an object changes
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"""
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_expire_for_fk_change(target, value, prop, colkey)
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