import inspect
import os
from abc import ABC, ABCMeta
from dataclasses import dataclass
from datetime import datetime, tzinfo
from types import FunctionType, WrapperDescriptorType
from typing import (
Any,
Callable,
Dict,
Generic,
Iterable,
List,
Optional,
Set,
Tuple,
Type,
TypeVar,
Union,
cast,
overload,
)
from uuid import UUID, uuid4
from eventsourcing.utils import get_method_name, get_topic, resolve_topic
# noinspection SpellCheckingInspection
TZINFO: tzinfo = resolve_topic(os.getenv("TZINFO_TOPIC", "datetime:timezone.utc"))
[docs]class MetaDomainEvent(ABCMeta):
[docs] def __new__(
mcs, name: str, bases: Tuple[type, ...], cls_dict: Dict[str, Any]
) -> "MetaDomainEvent":
event_cls = super().__new__(mcs, name, bases, cls_dict)
event_cls = dataclass(frozen=True)(event_cls) # type: ignore
return event_cls
T = TypeVar("T")
[docs]@dataclass(frozen=True)
class DomainEvent(ABC, Generic[T]):
"""
Base class for domain events, such as aggregate :class:`AggregateEvent`
and aggregate :class:`Snapshot`.
"""
originator_id: UUID
originator_version: int
timestamp: datetime
[docs] def mutate(self, aggregate: Optional[T]) -> Optional[T]:
"""Abstract mutator method."""
@staticmethod
def create_timestamp() -> datetime:
return datetime.now(tz=TZINFO)
TDomainEvent = TypeVar("TDomainEvent", bound=DomainEvent[Any])
TAggregate = TypeVar("TAggregate", bound="Aggregate")
[docs]class AggregateEvent(DomainEvent[TAggregate], metaclass=MetaDomainEvent):
"""
Base class for aggregate events. Subclasses will model
decisions made by the domain model aggregates.
"""
[docs] def mutate(self, aggregate: Optional[TAggregate]) -> Optional[TAggregate]:
"""
Changes the state of the aggregate
according to domain event attributes.
"""
assert aggregate is not None
# Check this event belongs to this aggregate.
if self.originator_id != aggregate.id:
raise OriginatorIDError(self.originator_id, aggregate.id)
# Check this event is the next in its sequence.
next_version = aggregate.version + 1
if self.originator_version != next_version:
raise OriginatorVersionError(self.originator_version, next_version)
# Call apply() before mutating values, in case exception is raised.
self.apply(aggregate)
# Update the aggregate version.
aggregate.version = self.originator_version
# Update the modified time.
aggregate.modified_on = self.timestamp
# Return the mutated aggregate.
return aggregate
[docs] def apply(self, aggregate: TAggregate) -> None:
"""
Applies the domain event to the aggregate.
"""
[docs]class AggregateCreated(AggregateEvent[TAggregate]):
# noinspection PyUnresolvedReferences
"""
Domain event for when aggregate is created.
Constructor arguments:
:param UUID originator_id: ID of originating aggregate.
:param int originator_version: version of originating aggregate.
:param datetime timestamp: date-time of the event
:param str originator_topic: topic for the aggregate class
"""
originator_topic: str
[docs] def mutate(self, aggregate: Optional[TAggregate]) -> Optional[TAggregate]:
"""
Constructs aggregate instance defined
by domain event object attributes.
"""
assert aggregate is None
# Resolve originator topic.
aggregate_class: Type[TAggregate] = resolve_topic(
self.__dict__["originator_topic"]
)
# Construct and return aggregate object.
agg = aggregate_class.__new__(aggregate_class)
# Separate the base class keywords arguments.
base_kwargs = _select_kwargs_mentioned_in_sig(self.__dict__, agg.__base_init__)
# Call the base class init method.
agg.__base_init__(**base_kwargs)
# Select values that aren't mentioned in the method signature.
init_kwargs = _select_kwargs_mentioned_in_sig(self.__dict__, agg.__init__)
# Provide the id, if the init method expects it.
if aggregate_class in _init_mentions_id:
init_kwargs["id"] = self.__dict__["originator_id"]
# Call the aggregate class init method.
agg.__init__(**init_kwargs) # noinspection PyArgumentList
self.apply(agg)
return agg
def _select_kwargs_mentioned_in_sig(
kwargs: Dict[str, Any], method: Callable[..., Any]
) -> Dict[str, Any]:
method_signature = inspect.signature(method)
names = set(method_signature.parameters)
return {k: v for k, v in kwargs.items() if k in names}
EventSpecType = Optional[Union[str, Type[AggregateEvent[Any]]]]
AnyCallable = Callable[..., None]
DecoratedObjType = TypeVar("DecoratedObjType", bound=Union[AnyCallable, property])
InjectEventType = bool
class CommandMethodDecorator:
def __init__(
self,
event_spec: EventSpecType,
decorated_obj: DecoratedObjType,
):
self.is_name_inferred_from_method = False
self.given_event_cls: Optional[Type[AggregateEvent[Any]]] = None
self.event_cls_name: Optional[str] = None
self.decorated_property: Optional[property] = None
self.is_property_setter = False
self.property_setter_arg_name: Optional[str] = None
self.decorated_method: AnyCallable
# Event name has been specified.
if isinstance(event_spec, str):
if event_spec == "":
raise ValueError("Can't use empty string as name of event class")
self.event_cls_name = event_spec
# Event class has been specified.
elif isinstance(event_spec, type) and issubclass(event_spec, AggregateEvent):
self.given_event_cls = event_spec
if self.given_event_cls in given_event_classes:
name = self.given_event_cls.__name__
raise TypeError(f"{name} event class used in more than one decorator")
else:
given_event_classes.add(self.given_event_cls)
# Process a decorated property.
if isinstance(decorated_obj, property):
# Disallow putting event decorator on property getter.
if decorated_obj.fset is None:
assert decorated_obj.fget, "Property has no getter"
method_name = decorated_obj.fget.__name__
raise TypeError(
f"@event can't decorate {method_name}() property getter"
)
# Remember we are decorating a property.
self.decorated_property = decorated_obj
# Remember the decorated method as the "setter" of the property.
self.decorated_method = decorated_obj.fset
assert isinstance(self.decorated_method, FunctionType)
# Disallow deriving event class names from property names.
if not self.given_event_cls and not self.event_cls_name:
method_name = self.decorated_method.__name__
raise TypeError(
f"@event on {method_name}() setter requires event name or class"
)
# Remember the name of the second setter arg.
setter_arg_names = list(inspect.signature(self.decorated_method).parameters)
assert len(setter_arg_names) == 2
self.property_setter_arg_name = setter_arg_names[1]
# Process a decorated method.
elif isinstance(decorated_obj, FunctionType):
# Remember the decorated method as the decorated object.
self.decorated_method = decorated_obj
# If necessary, derive an event class name from the method.
if not self.given_event_cls and not self.event_cls_name:
original_method_name = self.decorated_method.__name__
if original_method_name != "__init__":
self.is_name_inferred_from_method = True
self.event_cls_name = "".join(
[s.capitalize() for s in original_method_name.split("_")]
)
# Disallow decorating other types of object.
else:
raise TypeError(f"{decorated_obj} is not a function or property")
# Disallow using methods with variable params to define event class.
if self.event_cls_name:
_check_no_variable_params(self.decorated_method)
def __call__(self, *args: Any, **kwargs: Any) -> None:
# Initialised decorator was called directly, presumably by
# a decorating property that has this decorator as its fset.
# So trigger an event.
assert self.is_property_setter
assert self.property_setter_arg_name
assert len(args) == 2
assert len(kwargs) == 0
assert isinstance(args[0], Aggregate)
aggregate_instance = args[0]
bound = BoundCommandMethodDecorator(self, aggregate_instance)
property_setter_arg_value = args[1]
kwargs = {self.property_setter_arg_name: property_setter_arg_value}
bound.trigger(**kwargs)
@overload
def __get__(
self, instance: None, owner: "MetaAggregate"
) -> Union["UnboundCommandMethodDecorator", property]:
... # pragma: no cover
@overload
def __get__(
self, instance: "Aggregate", owner: "MetaAggregate"
) -> Union["BoundCommandMethodDecorator", Any]:
... # pragma: no cover
def __get__(
self, instance: Optional["Aggregate"], owner: "MetaAggregate"
) -> Union[
"BoundCommandMethodDecorator", "UnboundCommandMethodDecorator", property, Any
]:
# If we are decorating a property, then delegate to the property's __get__.
if self.decorated_property:
return self.decorated_property.__get__(instance, owner)
# Return a "bound" command method decorator if we have an instance.
elif instance:
return BoundCommandMethodDecorator(self, instance)
# Return an "unbound" command method decorator if we have no instance.
else:
return UnboundCommandMethodDecorator(self)
def __set__(self, instance: "Aggregate", value: Any) -> None:
# Set decorated property indirectly by triggering an event.
assert self.property_setter_arg_name
b = BoundCommandMethodDecorator(self, instance)
kwargs = {self.property_setter_arg_name: value}
b.trigger(**kwargs)
# Called because specifying decorator params.
@overload
def event(arg: EventSpecType = None) -> Callable[[DecoratedObjType], DecoratedObjType]:
... # pragma: no cover
# Called because Python is actually decorating something.
@overload
def event(arg: DecoratedObjType) -> DecoratedObjType:
... # pragma: no cover
[docs]def event(
arg: Union[EventSpecType, DecoratedObjType] = None,
) -> Union[Callable[[DecoratedObjType], DecoratedObjType], DecoratedObjType]:
"""
Can be used to decorate an aggregate method so that when the
method is called an event is triggered. The body of the method
will be used to apply the event to the aggregate, both when the
event is triggered and when the aggregate is reconstructed from
stored events.
.. code-block:: python
class MyAggregate(Aggregate):
@event("NameChanged")
def set_name(self, name: str):
self.name = name
...is equivalent to...
.. code-block:: python
class MyAggregate(Aggregate):
def set_name(self, name: str):
self.trigger_event(self.NameChanged, name=name)
class NameChanged(Aggregate.Event):
name: str
def apply(self, aggregate):
aggregate.name = self.name
In the example above, the event "NameChanged" is defined automatically
by inspecting the signature of the `set_name()` method. If it is
preferred to declare the event class explicitly, for example to define
upcasting of old events, the event class itself can be mentioned in the
event decorator rather than just providing the name of the event as a
string.
.. code-block:: python
class MyAggregate(Aggregate):
class NameChanged(Aggregate.Event):
name: str
@event(NameChanged)
def set_name(self, name: str):
aggregate.name = self.name
"""
if isinstance(arg, FunctionType) or isinstance(arg, property):
command_method_decorator = CommandMethodDecorator(
event_spec=None,
decorated_obj=arg,
)
return cast(
Callable[[DecoratedObjType], DecoratedObjType], command_method_decorator
)
elif (
arg is None
or isinstance(arg, str)
or isinstance(arg, type)
and issubclass(arg, AggregateEvent)
):
event_spec = arg
def create_command_method_decorator(
decorated_obj: DecoratedObjType,
) -> DecoratedObjType:
command_method_decorator = CommandMethodDecorator(
event_spec=event_spec,
decorated_obj=decorated_obj,
)
return cast(DecoratedObjType, command_method_decorator)
return create_command_method_decorator
else:
raise TypeError(
f"{arg} is not a str, aggregate event class, function, or property"
)
triggers = event
[docs]class UnboundCommandMethodDecorator:
"""
Wraps an EventDecorator instance when attribute is accessed
on an aggregate class.
"""
[docs] def __init__(self, event_decorator: CommandMethodDecorator):
"""
:param CommandMethodDecorator event_decorator:
"""
self.event_decorator = event_decorator
assert event_decorator.decorated_method
self.__qualname__ = event_decorator.decorated_method.__qualname__
self.__name__ = event_decorator.decorated_method.__name__
[docs]class BoundCommandMethodDecorator:
"""
Wraps an EventDecorator instance when attribute is accessed
on an aggregate so that the aggregate methods can be accessed.
"""
[docs] def __init__(
self, event_decorator: CommandMethodDecorator, aggregate: "TAggregate"
):
"""
:param CommandMethodDecorator event_decorator:
:param Aggregate aggregate:
"""
assert event_decorator.decorated_method
self.event_decorator = event_decorator
self.__qualname__ = event_decorator.decorated_method.__qualname__
self.__name__ = event_decorator.decorated_method.__name__
self.aggregate = aggregate
def trigger(self, *args: Any, **kwargs: Any) -> None:
assert isinstance(self.event_decorator, CommandMethodDecorator) # for PyCharm
assert self.event_decorator.decorated_method
kwargs = _coerce_args_to_kwargs(
self.event_decorator.decorated_method, args, kwargs
)
event_cls = decorated_event_classes[self.event_decorator]
kwargs = _select_kwargs_mentioned_in_sig(kwargs, event_cls.__dict__["__init__"])
self.aggregate.trigger_event(event_cls, **kwargs)
[docs] def __call__(self, *args: Any, **kwargs: Any) -> None:
self.trigger(*args, **kwargs)
given_event_classes: Set[type] = set()
decorated_methods: Dict[type, AnyCallable] = {}
aggregate_has_many_created_event_classes: Dict[type, List[str]] = {}
[docs]class DecoratedEvent(AggregateEvent[Any]):
[docs] def apply(self, aggregate: "TAggregate") -> None:
"""
Applies event to aggregate by calling method decorated by @event.
"""
# Call super method, just in case any base classes need it.
super().apply(aggregate)
# Identify the method that was decorated.
decorated_method = decorated_methods[type(self)]
# Select event attributes mentioned in method signature.
kwargs = _select_kwargs_mentioned_in_sig(self.__dict__, decorated_method)
# Call the original method with event attribute values.
decorated_method(aggregate, **kwargs)
decorated_event_classes: Dict[CommandMethodDecorator, Type[DecoratedEvent]] = {}
def _check_no_variable_params(method: FunctionType) -> None:
for param in inspect.signature(method).parameters.values():
if param.kind is param.VAR_POSITIONAL:
raise TypeError(
f"*{param.name} not supported by decorator on {method.__name__}()"
)
# Todo: Support VAR_POSITIONAL?
# annotations["__star_args__"] = "typing.Any"
elif param.kind is param.VAR_KEYWORD:
# Todo: Support VAR_KEYWORD?
# annotations["__star_kwargs__"] = "typing.Any"
raise TypeError(
f"**{param.name} not supported by decorator on {method.__name__}()"
)
def _coerce_args_to_kwargs(
method: AnyCallable,
args: Iterable[Any],
kwargs: Dict[str, Any],
expects_id: bool = False,
) -> Dict[str, Any]:
assert isinstance(method, (FunctionType, WrapperDescriptorType))
method_signature = inspect.signature(method)
copy_kwargs = dict(kwargs)
args = tuple(args)
positional_names = []
keyword_defaults = {}
required_positional = []
required_keyword_only = []
if expects_id:
positional_names.append("id")
required_positional.append("id")
for name, param in method_signature.parameters.items():
if name == "self":
continue
# elif param.kind in (param.POSITIONAL_ONLY, param.POSITIONAL_OR_KEYWORD):
if param.kind is param.KEYWORD_ONLY:
required_keyword_only.append(name)
if param.kind is param.POSITIONAL_OR_KEYWORD:
positional_names.append(name)
if param.default == param.empty:
required_positional.append(name)
if param.default != param.empty:
keyword_defaults[name] = param.default
# if not required_keyword_only and not positional_names:
# if args or kwargs:
# raise TypeError(f"{method.__name__}() takes no args")
for name in kwargs:
if name not in required_keyword_only and name not in positional_names:
raise TypeError(
f"{get_method_name(method)}() got an unexpected "
f"keyword argument '{name}'"
)
counter = 0
len_args = len(args)
if len_args > len(positional_names):
msg = (
f"{get_method_name(method)}() takes {len(positional_names) + 1} "
f"positional argument{'' if len(positional_names) + 1 == 1 else 's'} "
f"but {len_args + 1} were given"
)
raise TypeError(msg)
required_positional_not_in_kwargs = [
n for n in required_positional if n not in kwargs
]
num_missing = len(required_positional_not_in_kwargs) - len_args
if num_missing > 0:
missing_names = [
f"'{name}'" for name in required_positional_not_in_kwargs[len_args:]
]
msg = (
f"{get_method_name(method)}() missing {num_missing} required positional "
f"argument{'' if num_missing == 1 else 's'}: "
)
raise_missing_names_type_error(missing_names, msg)
for name in positional_names:
if counter + 1 > len_args:
break
if name not in kwargs:
copy_kwargs[name] = args[counter]
counter += 1
else:
raise TypeError(
f"{get_method_name(method)}() got multiple values for argument '{name}'"
)
missing_keyword_only_arguments = []
for name in required_keyword_only:
if name not in kwargs:
missing_keyword_only_arguments.append(name)
if missing_keyword_only_arguments:
missing_names = [f"'{name}'" for name in missing_keyword_only_arguments]
msg = (
f"{get_method_name(method)}() missing {len(missing_names)} "
f"required keyword-only argument"
f"{'' if len(missing_names) == 1 else 's'}: "
)
raise_missing_names_type_error(missing_names, msg)
for name, value in keyword_defaults.items():
if name not in copy_kwargs:
copy_kwargs[name] = value
return copy_kwargs
def raise_missing_names_type_error(missing_names: List[str], msg: str) -> None:
msg += missing_names[0]
if len(missing_names) == 2:
msg += f" and {missing_names[1]}"
elif len(missing_names) > 2:
msg += ", " + ", ".join(missing_names[1:-1])
msg += f", and {missing_names[-1]}"
raise TypeError(msg)
TT = TypeVar("TT", bound="type")
_annotations_mention_id: Set["MetaAggregate"] = set()
_init_mentions_id: Set["MetaAggregate"] = set()
[docs]class Aggregate(ABC, metaclass=MetaAggregate):
"""
Base class for aggregate roots.
"""
[docs] def __base_init__(
self, originator_id: UUID, originator_version: int, timestamp: datetime
) -> None:
"""
Initialises an aggregate object with an :data:`id`, a :data:`version`
number, and a :data:`timestamp`.
"""
self._id = originator_id
self._version = originator_version
self._created_on = timestamp
self._modified_on = timestamp
self._pending_events: List[AggregateEvent[Any]] = []
@property
def id(self) -> UUID:
"""
The ID of the aggregate.
"""
return self._id
@property
def version(self) -> int:
"""
The version number of the aggregate.
"""
return self._version
@version.setter
def version(self, version: int) -> None:
# noinspection PyAttributeOutsideInit
self._version = version
@property
def created_on(self) -> datetime:
"""
The date and time when the aggregate was created.
"""
return self._created_on
@property
def modified_on(self) -> datetime:
"""
The date and time when the aggregate was last modified.
"""
return self._modified_on
@modified_on.setter
def modified_on(self, modified_on: datetime) -> None:
# noinspection PyAttributeOutsideInit
self._modified_on = modified_on
@property
def pending_events(self) -> List[AggregateEvent[Any]]:
"""
A list of pending events.
"""
return self._pending_events
[docs] class Event(AggregateEvent[TAggregate]):
pass
[docs] class Created(Event[TAggregate], AggregateCreated[TAggregate]):
pass
[docs] def __new__(cls, *args: Any, **kwargs: Any) -> Any:
return object.__new__(cls)
[docs] def __eq__(self, other: Any) -> bool:
return type(self) == type(other) and self.__dict__ == other.__dict__
[docs] def __repr__(self) -> str:
attrs = [
f"{k.lstrip('_')}={v!r}"
for k, v in self.__dict__.items()
if k != "_pending_events"
]
return f"{type(self).__name__}({', '.join(attrs)})"
[docs] def trigger_event(
self,
event_class: Type[AggregateEvent[Any]],
**kwargs: Any,
) -> None:
"""
Triggers domain event of given type, by creating
an event object and using it to mutate the aggregate.
"""
# Construct the domain event as the
# next in the aggregate's sequence.
# Use counting to generate the sequence.
next_version = self.version + 1
# Impose the required common domain event attribute values.
kwargs = kwargs.copy()
kwargs.update(
originator_id=self.id,
originator_version=next_version,
timestamp=event_class.create_timestamp(),
)
try:
new_event = event_class(**kwargs)
except TypeError as e:
raise TypeError(f"Can't construct event {event_class}: {e}")
# Mutate aggregate with domain event.
new_event.mutate(self)
# Append the domain event to pending list.
self.pending_events.append(new_event)
[docs] def collect_events(self) -> List[AggregateEvent[Any]]:
"""
Collects and returns a list of pending aggregate
:class:`AggregateEvent` objects.
"""
collected = []
while self.pending_events:
collected.append(self.pending_events.pop(0))
return collected
# @overload
# def aggregate(*, created_event_name: str) -> Callable[[Any], Type[Aggregate]]:
# ...
#
#
# @overload
# def aggregate(cls: Any) -> Type[Aggregate]:
# ...
[docs]def aggregate(
cls: Optional[Any] = None,
*,
created_event_name: Optional[str] = None,
) -> Union[Type[Aggregate], Callable[[Any], Type[Aggregate]]]:
"""
Converts the class that was passed in to inherit from Aggregate.
.. code-block:: python
@aggregate
class MyAggregate:
pass
...is equivalent to...
.. code-block:: python
class MyAggregate(Aggregate):
pass
"""
def decorator(cls_: Any) -> Type[Aggregate]:
if issubclass(cls_, Aggregate):
raise TypeError(f"{cls_.__name__} is already an Aggregate")
bases = cls_.__bases__
if bases == (object,):
bases = (Aggregate,)
else:
bases += (Aggregate,)
cls_dict = dict()
cls_dict.update(cls_.__dict__)
cls_ = MetaAggregate(
cls_.__name__,
bases,
cls_dict,
created_event_name=created_event_name,
)
assert issubclass(cls_, Aggregate)
return cls_
if cls:
return decorator(cls)
else:
return decorator
[docs]class OriginatorIDError(Exception):
"""
Raised when a domain event can't be applied to
an aggregate due to an ID mismatch indicating
the domain event is not in the aggregate's
sequence of events.
"""
[docs]class OriginatorVersionError(Exception):
"""
Raised when a domain event can't be applied to
an aggregate due to version mismatch indicating
the domain event is not the next in the aggregate's
sequence of events.
"""
[docs]class VersionError(OriginatorVersionError):
"""
Old name for 'OriginatorVersionError'.
This class exists to maintain backwards-compatibility
but will be removed in a future version Please use
'OriginatorVersionError' instead.
"""
[docs]class Snapshot(DomainEvent[TAggregate], metaclass=MetaDomainEvent):
# noinspection PyUnresolvedReferences
"""
Snapshots represent the state of an aggregate at a particular
version.
Constructor arguments:
:param UUID originator_id: ID of originating aggregate.
:param int originator_version: version of originating aggregate.
:param datetime timestamp: date-time of the event
:param str topic: string that includes a class and its module
:param dict state: version of originating aggregate.
"""
topic: str
state: Dict[str, Any]
[docs] @classmethod
def take(cls, aggregate: TAggregate) -> "Snapshot[TAggregate]":
"""
Creates a snapshot of the given :class:`Aggregate` object.
"""
aggregate_state = dict(aggregate.__dict__)
aggregate_state.pop("_pending_events")
class_version = getattr(type(aggregate), "class_version", 1)
if class_version > 1:
aggregate_state["class_version"] = class_version
originator_id = aggregate_state.pop("_id")
originator_version = aggregate_state.pop("_version")
# noinspection PyArgumentList
return cls( # type: ignore
originator_id=originator_id,
originator_version=originator_version,
timestamp=cls.create_timestamp(),
topic=get_topic(type(aggregate)),
state=aggregate_state,
)
[docs] def mutate(self, _: Optional[TAggregate]) -> TAggregate:
"""
Reconstructs the snapshotted :class:`Aggregate` object.
"""
cls = resolve_topic(self.topic)
assert issubclass(cls, Aggregate)
aggregate_state = dict(self.state)
from_version = aggregate_state.pop("class_version", 1)
class_version = getattr(cls, "class_version", 1)
while from_version < class_version:
upcast_name = f"upcast_v{from_version}_v{from_version + 1}"
upcast = getattr(cls, upcast_name)
upcast(aggregate_state)
from_version += 1
aggregate_state["_id"] = self.originator_id
aggregate_state["_version"] = self.originator_version
aggregate_state["_pending_events"] = []
aggregate: TAggregate = object.__new__(cls)
aggregate.__dict__.update(aggregate_state)
return aggregate