1 # Copyright (c) 2014 The Chromium OS Authors. All rights reserved. 2 # Use of this source code is governed by a BSD-style license that can be 3 # found in the LICENSE file. 4 5 """Django database Router 6 7 Django gets configured with three database connections in frontend/settings.py. 8 - The default database 9 - This database should be used for most things. 10 - For the master, this is the global database. 11 - For shards, this this is the shard-local database. 12 - The global database 13 - For the master, this is the same database as default, which is the global 14 database. 15 - For the shards, this is the global database (the same as for the master). 16 - The readonly connection 17 - This should be the same database as the global database, but it should 18 use an account on the database that only has readonly permissions. 19 - The server database 20 - This is the database stores information about all servers in the Autotest 21 instance. Each instance, master or shard should have its own server 22 database is use_server_db is enabled in global config. 23 24 The reason shards need two distinct databases for different objects is, that 25 the tko parser should always write to the global database. Otherwise test 26 results wouldn't be synced back to the master and would not be accessible in one 27 place. 28 29 Therefore this class will route all queries for tables starts with `server` 30 prefix to server database, route all queries for tables that involve 31 `tko_`-prefixed tables to the global database. For all others this router will 32 not give a hint, which means the default database will be used. 33 """ 34 35 class Router(object): 36 """ 37 Decide if an object should be written to the default or to the global db. 38 39 This is an implementaton of Django's multi-database router interface: 40 https://docs.djangoproject.com/en/1.5/topics/db/multi-db/ 41 """ 42 43 def _should_be_in_server_db(self, model): 44 """Return True if the model should be stored in the server db. 45 46 @param model: Model to decide for. 47 48 @return: True if querying the model requires server database. 49 """ 50 return model._meta.db_table.startswith('server') 51 52 53 def _should_be_in_global(self, model): 54 """Returns True if the model should be stored in the global db. 55 56 @param model: Model to decide for. 57 58 @return: True if querying the model requires global database. 59 """ 60 return model._meta.db_table.startswith('tko_') 61 62 63 def db_for_read(self, model, **hints): 64 """Return the database for a reading access. 65 66 @param model: Model to decide for. 67 @param hints: Optional arguments to determine which database for read. 68 69 @returns: 'server' for all server models. 'global' for all tko models, 70 None otherwise. None means the router doesn't have an opinion. 71 """ 72 if self._should_be_in_server_db(model): 73 return 'server' 74 if self._should_be_in_global(model): 75 return 'global' 76 return None 77 78 79 def db_for_write(self, model, **hints): 80 """Return the database for a writing access. 81 82 @param model: Model to decide for. 83 @param hints: Optional arguments to determine which database for write. 84 85 @returns: 'server' for all server models. 'global' for all tko models, 86 None otherwise. None means the router doesn't have an opinion. 87 """ 88 if self._should_be_in_server_db(model): 89 return 'server' 90 if self._should_be_in_global(model): 91 return 'global' 92 return None 93 94 95 def allow_relation(self, obj1, obj2, **hints): 96 """ 97 Allow relations only if either both are in tko_ tables or none is. 98 99 @param obj1: First object involved in the relation. 100 @param obj2: Second object involved in the relation. 101 @param hints: Optional arguments to determine if relation is allowed. 102 103 @returns False, if the relation should be prohibited, 104 None, if the router doesn't have an opinion. 105 """ 106 if (not self._should_be_in_server_db(type(obj1)) == 107 self._should_be_in_server_db(type(obj2))): 108 return False 109 if (not self._should_be_in_global(type(obj1)) == 110 self._should_be_in_global(type(obj2))): 111 return False 112 return None 113
