| # Copyright (c) 2014 The Chromium OS Authors. All rights reserved. |
| # Use of this source code is governed by a BSD-style license that can be |
| # found in the LICENSE file. |
| |
| """Django database Router |
| |
| Django gets configured with three database connections in frontend/settings.py. |
| - The default database |
| - This database should be used for most things. |
| - For the main, this is the global database. |
| - For shards, this this is the shard-local database. |
| - The global database |
| - For the main, this is the same database as default, which is the global |
| database. |
| - For the shards, this is the global database (the same as for the main). |
| - The readonly connection |
| - This should be the same database as the global database, but it should |
| use an account on the database that only has readonly permissions. |
| - The server database |
| - This is the database stores information about all servers in the Autotest |
| instance. Each instance, main or shard should have its own server |
| database is use_server_db is enabled in global config. |
| |
| The reason shards need two distinct databases for different objects is, that |
| the tko parser should always write to the global database. Otherwise test |
| results wouldn't be synced back to the main and would not be accessible in one |
| place. |
| |
| Therefore this class will route all queries for tables starts with `server` |
| prefix to server database, route all queries for tables that involve |
| `tko_`-prefixed tables to the global database. For all others this router will |
| not give a hint, which means the default database will be used. |
| """ |
| |
| class Router(object): |
| """ |
| Decide if an object should be written to the default or to the global db. |
| |
| This is an implementaton of Django's multi-database router interface: |
| https://docs.djangoproject.com/en/1.5/topics/db/multi-db/ |
| """ |
| |
| def _should_be_in_server_db(self, model): |
| """Return True if the model should be stored in the server db. |
| |
| @param model: Model to decide for. |
| |
| @return: True if querying the model requires server database. |
| """ |
| return model._meta.db_table.startswith('server') |
| |
| |
| def _should_be_in_global(self, model): |
| """Returns True if the model should be stored in the global db. |
| |
| @param model: Model to decide for. |
| |
| @return: True if querying the model requires global database. |
| """ |
| return model._meta.db_table.startswith('tko_') |
| |
| |
| def db_for_read(self, model, **hints): |
| """Return the database for a reading access. |
| |
| @param model: Model to decide for. |
| @param hints: Optional arguments to determine which database for read. |
| |
| @returns: 'server' for all server models. 'global' for all tko models, |
| None otherwise. None means the router doesn't have an opinion. |
| """ |
| if self._should_be_in_server_db(model): |
| return 'server' |
| if self._should_be_in_global(model): |
| return 'global' |
| return None |
| |
| |
| def db_for_write(self, model, **hints): |
| """Return the database for a writing access. |
| |
| @param model: Model to decide for. |
| @param hints: Optional arguments to determine which database for write. |
| |
| @returns: 'server' for all server models. 'global' for all tko models, |
| None otherwise. None means the router doesn't have an opinion. |
| """ |
| if self._should_be_in_server_db(model): |
| return 'server' |
| if self._should_be_in_global(model): |
| return 'global' |
| return None |
| |
| |
| def allow_relation(self, obj1, obj2, **hints): |
| """ |
| Allow relations only if either both are in tko_ tables or none is. |
| |
| @param obj1: First object involved in the relation. |
| @param obj2: Second object involved in the relation. |
| @param hints: Optional arguments to determine if relation is allowed. |
| |
| @returns False, if the relation should be prohibited, |
| None, if the router doesn't have an opinion. |
| """ |
| if (not self._should_be_in_server_db(type(obj1)) == |
| self._should_be_in_server_db(type(obj2))): |
| return False |
| if (not self._should_be_in_global(type(obj1)) == |
| self._should_be_in_global(type(obj2))): |
| return False |
| return None |