def take_snapshot(self, entity_id, until=None):
"""Takes a snapshot of the entity as it existed after
the most recent event, optionally until a given time.
"""
if self.snapshot_strategy is None:
raise ValueError(
"Can't take snapshots without a snapshot strategy.")
# Get the last event (optionally until a particular time).
last_event = self.get_most_recent_event(entity_id, until=until)
# If there aren't any events, there can't be a snapshot, so return None.
if last_event is None:
return None
# If there is something to snapshot, then look for
# the last snapshot before the last event.
last_event_id = last_event.domain_event_id
last_snapshot = self.get_snapshot(entity_id, until=last_event_id)
# If there's a snapshot...
if last_snapshot:
assert isinstance(last_snapshot,
AbstractSnapshop), type(last_snapshot)
# and it is coincident with the last event...
if last_snapshot.at_event_id == last_event_id:
# then there's nothing to do.
return last_snapshot
else:
# Otherwise there must be events after the snapshot, so
# remember to get events after the last event that was
# applied to the entity, and obtain the initial entity
# state so those event can be applied.
after_event_id = last_snapshot.at_event_id
initial_state = entity_from_snapshot(last_snapshot)
else:
# If there isn't a snapshot, start from scratch.
after_event_id = None
initial_state = None
# Get entity in the state after this event was applied.
entity = self.replay_events(entity_id,
after=after_event_id,
until=last_event_id,
initial_state=initial_state)
# Take a snapshot of the entity.
return self.snapshot_strategy.take_snapshot(entity,
at_event_id=last_event_id)
def get_entity(self, entity_id, until=None):
"""
Returns entity with given ID, optionally as it was until the given domain event ID.
"""
# Get a snapshot (None if none exist).
snapshot = self.event_player.get_snapshot(entity_id, until)
# Decide the initial state, and after when we need to get the events.
if snapshot is None:
after = None
initial_state = None
else:
after = snapshot.at_event_id
initial_state = entity_from_snapshot(snapshot)
# Replay domain events.
return self.event_player.replay_events(entity_id, after=after, until=until, initial_state=initial_state)
def take_snapshot(self, entity_id, until=None):
"""Takes a snapshot of the entity as it existed after
the most recent event, optionally until a given time.
"""
if self.snapshot_strategy is None:
raise ValueError("Can't take snapshots without a snapshot strategy.")
# Get the last event (optionally until a particular time).
last_event = self.get_most_recent_event(entity_id, until=until)
# If there aren't any events, there can't be a snapshot, so return None.
if last_event is None:
return None
# If there is something to snapshot, then look for
# the last snapshot before the last event.
last_event_id = last_event.domain_event_id
last_snapshot = self.get_snapshot(entity_id, until=last_event_id)
# If there's a snapshot...
if last_snapshot:
assert isinstance(last_snapshot, AbstractSnapshop), type(last_snapshot)
# and it is coincident with the last event...
if last_snapshot.at_event_id == last_event_id:
# then there's nothing to do.
return last_snapshot
else:
# Otherwise there must be events after the snapshot, so
# remember to get events after the last event that was
# applied to the entity, and obtain the initial entity
# state so those event can be applied.
after_event_id = last_snapshot.at_event_id
initial_state = entity_from_snapshot(last_snapshot)
else:
# If there isn't a snapshot, start from scratch.
after_event_id = None
initial_state = None
# Get entity in the state after this event was applied.
entity = self.replay_events(entity_id, after=after_event_id, until=last_event_id, initial_state=initial_state)
# Take a snapshot of the entity.
return self.snapshot_strategy.take_snapshot(entity, at_event_id=last_event_id)
def get_entity(self, entity_id, until=None):
"""
Returns entity with given ID, optionally as it was until the given domain event ID.
"""
# Get a snapshot (None if none exist).
snapshot = self.event_player.get_snapshot(entity_id, until)
# Decide the initial state, and after when we need to get the events.
if snapshot is None:
after = None
initial_state = None
else:
after = snapshot.at_event_id
initial_state = entity_from_snapshot(snapshot)
# Replay domain events.
return self.event_player.replay_events(entity_id,
after=after,
until=until,
initial_state=initial_state)
def test_snapshots(self):
stored_event_repo = PythonObjectsStoredEventRepository()
event_store = EventStore(stored_event_repo)
self.ps = PersistenceSubscriber(event_store)
event_player = EventPlayer(event_store=event_store,
id_prefix='Example',
mutate_func=Example.mutate)
# Create a new entity.
registered_example = register_new_example(a=123, b=234)
# Take a snapshot.
snapshot = take_snapshot(registered_example, uuid1().hex)
# Replay from this snapshot.
after = snapshot.at_event_id
initial_state = entity_from_snapshot(snapshot)
retrieved_example = event_player.replay_events(
registered_example.id, initial_state=initial_state, after=after)
# Check the attributes are correct.
self.assertEqual(retrieved_example.a, 123)
# Remember the time now.
timecheck1 = uuid1().hex
# Change attribute value.
retrieved_example.a = 999
# Check the initial state doesn't move.
self.assertEqual(initial_state.a, 123)
# Remember the time now.
timecheck2 = uuid1().hex
# Change attribute value.
retrieved_example.a = 9999
# Remember the time now.
timecheck3 = uuid1().hex
# Check the event sourced entities are correct.
assert initial_state.a == 123
retrieved_example = event_player.replay_events(registered_example.id)
self.assertEqual(retrieved_example.a, 9999)
# Take another snapshot.
snapshot2 = take_snapshot(retrieved_example, uuid1().hex)
# Check we can replay from this snapshot.
initial_state2 = entity_from_snapshot(snapshot2)
after2 = snapshot2.domain_event_id
retrieved_example = event_player.replay_events(
registered_example.id, initial_state=initial_state2, after=after2)
# Check the attributes are correct.
self.assertEqual(retrieved_example.a, 9999)
# Check we can get historical state at timecheck1.
retrieved_example = event_player.replay_events(registered_example.id,
until=timecheck1)
self.assertEqual(retrieved_example.a, 123)
# Check we can get historical state at timecheck2.
retrieved_example = event_player.replay_events(registered_example.id,
until=timecheck2)
self.assertEqual(retrieved_example.a, 999)
# Check we can get historical state at timecheck3.
retrieved_example = event_player.replay_events(registered_example.id,
until=timecheck3)
self.assertEqual(retrieved_example.a, 9999)
# Similarly, check we can get historical state using a snapshot
retrieved_example = event_player.replay_events(
registered_example.id,
initial_state=initial_state,
after=after,
until=timecheck2)
self.assertEqual(retrieved_example.a, 999)
def test_snapshots(self):
stored_event_repo = PythonObjectsStoredEventRepository()
event_store = EventStore(stored_event_repo)
self.ps = PersistenceSubscriber(event_store)
event_player = EventPlayer(event_store=event_store, id_prefix='Example', mutate_func=Example.mutate)
# Create a new entity.
registered_example = register_new_example(a=123, b=234)
# Take a snapshot.
snapshot = take_snapshot(registered_example, uuid1().hex)
# Replay from this snapshot.
after = snapshot.at_event_id
initial_state = entity_from_snapshot(snapshot)
retrieved_example = event_player.replay_events(registered_example.id, initial_state=initial_state, after=after)
# Check the attributes are correct.
self.assertEqual(retrieved_example.a, 123)
# Remember the time now.
timecheck1 = uuid1().hex
# Change attribute value.
retrieved_example.a = 999
# Check the initial state doesn't move.
self.assertEqual(initial_state.a, 123)
# Remember the time now.
timecheck2 = uuid1().hex
# Change attribute value.
retrieved_example.a = 9999
# Remember the time now.
timecheck3 = uuid1().hex
# Check the event sourced entities are correct.
assert initial_state.a == 123
retrieved_example = event_player.replay_events(registered_example.id)
self.assertEqual(retrieved_example.a, 9999)
# Take another snapshot.
snapshot2 = take_snapshot(retrieved_example, uuid1().hex)
# Check we can replay from this snapshot.
initial_state2 = entity_from_snapshot(snapshot2)
after2 = snapshot2.domain_event_id
retrieved_example = event_player.replay_events(registered_example.id, initial_state=initial_state2, after=after2)
# Check the attributes are correct.
self.assertEqual(retrieved_example.a, 9999)
# Check we can get historical state at timecheck1.
retrieved_example = event_player.replay_events(registered_example.id, until=timecheck1)
self.assertEqual(retrieved_example.a, 123)
# Check we can get historical state at timecheck2.
retrieved_example = event_player.replay_events(registered_example.id, until=timecheck2)
self.assertEqual(retrieved_example.a, 999)
# Check we can get historical state at timecheck3.
retrieved_example = event_player.replay_events(registered_example.id, until=timecheck3)
self.assertEqual(retrieved_example.a, 9999)
# Similarly, check we can get historical state using a snapshot
retrieved_example = event_player.replay_events(registered_example.id, initial_state=initial_state, after=after, until=timecheck2)
self.assertEqual(retrieved_example.a, 999)