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..
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.
Convention for heading levels in Neutron devref:
======= Heading 0 (reserved for the title in a document)
------- Heading 1
~~~~~~~ Heading 2
+++++++ Heading 3
''''''' Heading 4
(Avoid deeper levels because they do not render well.)
DB Model Query
==============
The implementation in ``neutron_lib.db.model_query`` is intended to be used as a
stepping stone for existing consumers using standard database models/tables.
Moving forward new database implementations should all use neutron's Versioned
Object approach, while existing model based implementations should begin
migrating to Versioned Objects.
Registering Hooks
-----------------
The ``neutron_lib.db.model_query.register_hook`` function allows hooks to be
registered for invocation during a respective database query.
Each hook has three components:
- "query": used to build the query expression
- "filter": used to build the filter expression
- "result_filters": used for final filtering on the query result
Query hooks take as input the query being built and return a transformed
query expression. For example::
def mymodel_query_hook(context, original_model, query):
augmented_query = ...
return augmented_query
Filter hooks take as input the filter expression being built and return
a transformed filter expression. For example::
def mymodel_filter_hook(context, original_model, filters):
refined_filters = ...
return refined_filters
Result filter hooks take as input the query expression and the filter
expression, and return a final transformed query expression. For example::
def mymodel_result_filter_hook(query, filters):
final_filters = ...
return query.filter(final_filters)
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