def get_database_for_model_instance(instance):
if instance._state.db:
return instance._state.db
model = instance._meta.model
possible_databases = get_possible_databases_for_model(model=model)
if len(possible_databases) == 1:
return possible_databases[0]
elif len(possible_databases) == 0:
pass
else:
model_has_sharded_id_field = getattr(
model, 'django_sharding__sharded_by_field', None) is not None
if model_has_sharded_id_field:
sharded_by_field_id = getattr(
instance,
getattr(model, 'django_sharding__sharded_by_field',
'django_sharding__none'), None)
if sharded_by_field_id is not None:
return model.get_shard_from_id(sharded_by_field_id)
return instance.get_shard()
raise DjangoShardingException(
"Unable to deduce datbase for model instance")
def is_model_class_on_database(model, database):
specific_database = getattr(model, 'django_sharding__database', None)
is_sharded = getattr(model, 'django_sharding__is_sharded', False)
if specific_database and is_sharded:
raise DjangoShardingException('Model marked as both sharded and on a single database, unable to determine where to run migrations for {}.'.format(model.__class__.__name__))
if specific_database:
return getattr(model, 'django_sharding__database') == database
if is_sharded:
shard_group = getattr(model, 'django_sharding__shard_group', None)
if shard_group:
return settings.DATABASES[database]['SHARD_GROUP'] == shard_group
raise DjangoShardingException("Unable to determine what database the model is on as the shard group of {} is unknown.".format(model.__class__.__name__))
return database == "default"
def db_for_read(self, model, **hints):
possible_databases = get_possible_databases_for_model(model=model)
if len(possible_databases) == 1:
return possible_databases[0]
shard = self._get_shard(model, **hints)
if shard:
shard_group = getattr(model, 'django_sharding__shard_group', None)
if not shard_group:
raise DjangoShardingException('Unable to identify the shard_group for the {} model'.format(model))
routing_strategy = self.get_read_db_routing_strategy(shard_group)
return routing_strategy.pick_read_db(shard)
return None
def get_database_for_model_instance(instance):
if instance._state.db:
return instance._state.db
model = instance._meta.model
possible_databases = get_possible_databases_for_model(model=model)
if len(possible_databases) == 1:
return possible_databases[0]
elif len(possible_databases) == 0:
pass
else:
return instance.get_shard()
raise DjangoShardingException(
"Unable to deduce datbase for model instance")