from eventsourcing.domain.model.entity import AbstractEntityRepository
from eventsourcing.exceptions import RepositoryKeyError
from eventsourcing.infrastructure.eventplayer import EventPlayer
from eventsourcing.infrastructure.snapshotting import entity_from_snapshot
[docs]class EventSourcedRepository(EventPlayer, AbstractEntityRepository):
[docs] def __contains__(self, entity_id):
"""
Returns a boolean value according to whether entity with given ID exists.
"""
return self.get_entity(entity_id) is not None
[docs] def __getitem__(self, entity_id):
"""
Returns entity with given ID.
"""
if self._use_cache:
try:
# Get entity from the cache.
entity = self._cache[entity_id]
except KeyError:
# Reconstitute the entity.
entity = self.get_entity(entity_id)
# Put entity in the cache.
self._cache[entity_id] = entity
else:
entity = self.get_entity(entity_id)
# Never created or already discarded?
if entity is None:
raise RepositoryKeyError(entity_id)
# Return entity.
return entity
[docs] def get_entity(self, entity_id, at=None):
"""
Returns entity with given ID, optionally until position.
"""
# Get a snapshot (None if none exist).
if self._snapshot_strategy is not None:
snapshot = self._snapshot_strategy.get_snapshot(entity_id, lte=at)
else:
snapshot = None
# Decide the initial state of the entity, and the
# version of the last item applied to the entity.
if snapshot is None:
initial_state = None
gt = None
else:
initial_state = entity_from_snapshot(snapshot)
gt = snapshot.originator_version
# Obtain and return current state.
return self.get_and_project_events(entity_id, gt=gt, lte=at, initial_state=initial_state)
[docs] def get_and_project_events(self, entity_id, gt=None, gte=None, lt=None, lte=None, limit=None, initial_state=None,
query_descending=False):
"""
Reconstitutes requested domain entity from domain events found in event store.
"""
# Decide if query is in ascending order.
# - A "speed up" for when events are stored in descending order (e.g.
# in Cassandra) and it is faster to get them in that order.
# - This isn't useful when 'until' or 'after' or 'limit' are set,
# because the inclusiveness or exclusiveness of until and after
# and the end of the stream that is truncated by limit both depend on
# the direction of the query. Also paging backwards isn't useful, because
# all the events are needed eventually, so it would probably slow things
# down. Paging is intended to support replaying longer event streams, and
# only makes sense to work in ascending order.
if gt is None and gte is None and lt is None and lte is None and self.__page_size__ is None:
is_ascending = False
else:
is_ascending = not query_descending
# Get entity's domain events from the event store.
domain_events = self.event_store.get_domain_events(
originator_id=entity_id,
gt=gt,
gte=gte,
lt=lt,
lte=lte,
limit=limit,
is_ascending=is_ascending,
page_size=self.__page_size__
)
# The events will be replayed in ascending order.
if not is_ascending:
domain_events = list(reversed(list(domain_events)))
# Project the domain events onto the initial state.
return self.project_events(initial_state, domain_events)
# Todo: Does this method belong on this class?
[docs] def take_snapshot(self, entity_id, lt=None, lte=None):
"""
Takes a snapshot of the entity as it existed after the most recent
event, optionally less than, or less than or equal to, a particular position.
"""
snapshot = None
if self._snapshot_strategy:
# Get the latest event (optionally until a particular position).
latest_event = self.event_store.get_most_recent_event(entity_id, lt=lt, lte=lte)
# If there is something to snapshot, then look for a snapshot
# taken before or at the entity version of the latest event. Please
# note, the snapshot might have a smaller version number than
# the latest event if events occurred since the latest snapshot was taken.
if latest_event is not None:
latest_snapshot = self._snapshot_strategy.get_snapshot(
entity_id, lt=lt, lte=lte
)
latest_version = latest_event.originator_version
if latest_snapshot and latest_snapshot.originator_version == latest_version:
# If up-to-date snapshot exists, there's nothing to do.
snapshot = latest_snapshot
else:
# Otherwise recover entity state from latest snapshot.
if latest_snapshot:
initial_state = entity_from_snapshot(latest_snapshot)
gt = latest_snapshot.originator_version
else:
initial_state = None
gt = None
# Fast-forward entity state to latest version.
entity = self.get_and_project_events(
entity_id=entity_id,
gt=gt,
lte=latest_version,
initial_state=initial_state,
)
# Take snapshot from entity.
snapshot = self._snapshot_strategy.take_snapshot(entity_id, entity, latest_version)
return snapshot