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