Relocation of Database Models

This document is intended to track and notify developers that db models in neutron will be centralized and moved to a new tree under neutron/db/models. This was discussed in [1]. The reason for relocating db models is to solve the cyclic import issue while implementing oslo versioned objects for resources in neutron.

The reason behind this relocation is Mixin class and db models for some resources in neutron are in same module. In Mixin classes, there are methods which provide functionality of fetching, adding, updating and deleting data via queries. These queries will be replaced with use of versioned objects and definition of versioned object will be using db models. So object files will be importing models and Mixin need to import those objects which will end up in cyclic import.

Structure of Model Definitions

We have decided to move all models definitions to neutron/db/models/ with no futher nesting after that point. The deprecation method to move models is already been added to avoid breakage of third party plugins using those models. All relocated models need to use deprecate method that will generate a warning and return new class for use of old class. Some examples of relocated models [2] and [3]. In future if you define new models please make sure they are separated from mixins and are under tree neutron/db/models/ .

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