from functools import reduce
from eventsourcing.infrastructure.eventstore import AbstractEventStore
from eventsourcing.infrastructure.snapshotting import AbstractSnapshotStrategy, entity_from_snapshot
# def clone_object(initial_state):
# initial_state_copy = object.__new__(type(initial_state))
# initial_state_copy.__dict__.update(deepcopy(initial_state.__dict__))
# return initial_state_copy
[docs]class EventPlayer(object):
"""
Reconstitutes domain entities from domain events
retrieved from the event store, optionally with snapshots.
"""
def __init__(self, event_store, mutator, page_size=None, is_short=False, snapshot_strategy=None):
assert isinstance(event_store, AbstractEventStore), event_store
if snapshot_strategy is not None:
assert isinstance(snapshot_strategy, AbstractSnapshotStrategy), snapshot_strategy
self.event_store = event_store
self.mutator = mutator
self.page_size = page_size
self.is_short = is_short
self.snapshot_strategy = snapshot_strategy
[docs] def replay_entity(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 self.is_short and 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 the domain events that are to be replayed.
domain_events = self.get_domain_events(entity_id,
gt=gt,
gte=gte,
lt=lt,
lte=lte,
limit=limit,
is_ascending=is_ascending
)
# The events will be replayed in ascending order.
if not is_ascending:
domain_events = reversed(list(domain_events))
# Replay the domain events, starting with the initial state.
return self.replay_events(initial_state, domain_events)
[docs] def get_domain_events(self, entity_id, gt=None, gte=None, lt=None, lte=None, limit=None, is_ascending=True):
"""
Returns domain events for given entity ID.
"""
# 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)
return domain_events
[docs] def replay_events(self, initial_state, domain_events):
"""
Mutates initial state using the sequence of domain events.
"""
return reduce(self.mutator, domain_events, initial_state)
[docs] def get_snapshot(self, entity_id, lt=None, lte=None):
"""
Returns a snapshot for given entity ID, according to the snapshot strategy.
"""
if self.snapshot_strategy:
return self.snapshot_strategy.get_snapshot(entity_id, lt=lt, lte=lte)
[docs] def get_most_recent_event(self, entity_id, lt=None, lte=None):
"""
Returns the most recent event for the given entity ID.
"""
return self.event_store.get_most_recent_event(entity_id, lt=lt, lte=lte)
[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.
"""
# assert isinstance(self.snapshot_strategy, AbstractSnapshotStrategy)
# Get the last event (optionally until a particular position).
last_event = self.get_most_recent_event(entity_id, lt=lt, lte=lte)
if last_event is None:
# If there aren't any events, there can't be a snapshot.
snapshot = None
else:
# If there is something to snapshot, then look for a snapshot
# taken before or at the entity version of the last event. Please
# note, the snapshot might have a smaller version number than
# the last event if events occurred since the last snapshot was taken.
last_version = last_event.originator_version
last_snapshot = self.get_snapshot(entity_id, lte=last_version)
if last_snapshot and last_snapshot.originator_version == last_version:
# If up-to-date snapshot exists, there's nothing to do.
snapshot = last_snapshot
else:
# Otherwise recover entity and take snapshot.
if last_snapshot:
initial_state = entity_from_snapshot(last_snapshot)
gt = last_snapshot.originator_version
else:
initial_state = None
gt = None
entity = self.replay_entity(entity_id, gt=gt, lte=last_version, initial_state=initial_state)
snapshot = self.snapshot_strategy.take_snapshot(entity_id, entity, last_version)
return snapshot