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import importlib
import inspect
from collections import defaultdict
from functools import partial
from typing import Any, Type, TypeVar
from seedwork.application.command_handlers import CommandResult
from seedwork.application.commands import Command
from seedwork.application.events import EventResult, EventResultSet, IntegrationEvent
from seedwork.application.exceptions import ApplicationException
from seedwork.application.inbox_outbox import InMemoryInbox
from seedwork.application.queries import Query
from seedwork.application.query_handlers import QueryResult
from seedwork.domain.events import DomainEvent
from seedwork.domain.repositories import GenericRepository
from seedwork.utils.data_structures import OrderedSet
def get_function_arguments(func):
handler_signature = inspect.signature(func)
kwargs_iterator = iter(handler_signature.parameters.items())
_, first_param = next(kwargs_iterator)
first_parameter = first_param.annotation
remaining_parameters = {}
for name, param in kwargs_iterator:
remaining_parameters[name] = param.annotation
return first_parameter, remaining_parameters
T = TypeVar("T", CommandResult, EventResult)
def collect_domain_events(result: T, handler_kwargs) -> T:
domain_events = []
repositories = filter(
lambda x: isinstance(x, GenericRepository), handler_kwargs.values()
)
for repo in repositories:
domain_events.extend(repo.collect_events())
result.events.extend(domain_events)
return result
class DependencyProvider:
"""Basic dependency provider that uses a dictionary to store and inject dependencies"""
def __init__(self, **kwargs):
self.dependencies = kwargs
def register_dependency(self, identifier, dependency_instance):
self.dependencies[identifier] = dependency_instance
def get_dependency(self, identifier):
return self.dependencies[identifier]
def _get_arguments(self, func):
return get_function_arguments(func)
def _resolve_arguments(self, handler_parameters) -> dict:
"""Match handler_parameters with dependencies"""
kwargs = {}
for param_name, param_type in handler_parameters.items():
try:
if param_type is inspect._empty:
raise ValueError("No type annotation")
kwargs[param_name] = self.get_dependency(param_type)
continue
except (ValueError, KeyError):
pass
try:
kwargs[param_name] = self.get_dependency(param_name)
continue
except (ValueError, KeyError):
pass
return kwargs
def get_handler_kwargs(self, func, **overrides):
_, handler_parameters = self._get_arguments(func)
kwargs = self._resolve_arguments(handler_parameters)
kwargs.update(**overrides)
return kwargs
def __getitem__(self, key):
return self.get_dependency(key)
def __setitem__(self, key, value):
self.register_dependency(key, value)
class TransactionContext:
"""A context spanning a single transaction for execution of commands and queries
Typically, the following thing happen in a transaction context:
- a command handler is called, which results in aggregate changes that fire domain events
- a domain event is raised, after
- a domain event handler is called
- a command is executed
"""
def __init__(self, app, **overrides):
self.app = app
self.overrides = overrides
self.dependency_provider = app.dependency_provider
self.task = None
self.next_commands = []
self.integration_events = []
def __enter__(self):
"""Should be used to start a transaction"""
self.app._on_enter_transaction_context(self)
return self
def __exit__(self, exc_type, exc_val, exc_tb):
"""Should be used to commit/end a transaction"""
self.app._on_exit_transaction_context(self, exc_type, exc_val, exc_tb)
def _wrap_with_middlewares(
self, handler_func, command=None, query=None, event=None
):
p = handler_func
for middleware in self.app._transaction_middlewares:
p = partial(middleware, self, p, command, query, event)
return p
def execute_query(self, query) -> QueryResult:
assert (
self.task is None
), "Cannot execute query while another task is being executed"
self.task = query
handler_func = self.app.get_query_handler(query)
handler_kwargs = self.dependency_provider.get_handler_kwargs(
handler_func, **self.overrides
)
p = partial(handler_func, query, **handler_kwargs)
wrapped_handler = self._wrap_with_middlewares(p, query=query)
result = wrapped_handler()
assert isinstance(
result, QueryResult
), f"Got {result} instead of QueryResult from {handler_func}"
return result
def execute_command(self, command) -> CommandResult:
assert (
self.task is None
), "Cannot execute command while another task is being executed"
self.task = command
handler_func = self.app.get_command_handler(command)
handler_kwargs = self.dependency_provider.get_handler_kwargs(
handler_func, **self.overrides
)
p = partial(handler_func, command, **handler_kwargs)
wrapped_handler = self._wrap_with_middlewares(p, command=command)
# execute wrapped command handler
command_result = wrapped_handler() or CommandResult.success()
assert isinstance(
command_result, CommandResult
), f"Got {command_result} instead of CommandResult from {handler_func}"
command_result = collect_domain_events(command_result, handler_kwargs)
self.next_commands = []
self.integration_events = []
event_queue = command_result.events.copy()
while len(event_queue) > 0:
event = event_queue.pop(0)
if isinstance(event, IntegrationEvent):
self.collect_integration_event(event)
elif isinstance(event, DomainEvent):
event_results = self.handle_domain_event(event)
self.next_commands.extend(event_results.commands)
event_queue.extend(event_results.events)
return CommandResult.success(payload=command_result.payload)
def handle_domain_event(self, event) -> EventResultSet:
event_results = []
for handler_func in self.app.get_event_handlers(event):
handler_kwargs = self.dependency_provider.get_handler_kwargs(
handler_func, **self.overrides
)
p = partial(handler_func, event, **handler_kwargs)
wrapped_handler = self._wrap_with_middlewares(p, event=event)
event_result = wrapped_handler() or EventResult.success()
assert isinstance(
event_result, EventResult
), f"Got {event_result} instead of EventResult from {handler_func}"
event_result = collect_domain_events(event_result, handler_kwargs)
event_results.append(event_result)
return EventResultSet(event_results)
def collect_integration_event(self, event):
self.integration_events.append(event)
def get_service(self, service_cls) -> Any:
"""Get a dependency from the dependency provider"""
return self.dependency_provider.get_dependency(service_cls)
def __getitem__(self, item) -> Any:
return self.get_service(item)
@property
def current_user(self):
return self.dependency_provider.get_dependency("current_user")
class ApplicationModule:
def __init__(self, name, version=1.0):
self.name = name
self.version = version
self.command_handlers = {}
self.query_handlers = {}
self.event_handlers = defaultdict(OrderedSet)
def query_handler(self, handler_func):
"""Query handler decorator"""
query_cls, _ = get_function_arguments(handler_func)
self.query_handlers[query_cls] = handler_func
return handler_func
def command_handler(self, handler_func):
"""Command handler decorator"""
command_cls, _ = get_function_arguments(handler_func)
self.command_handlers[command_cls] = handler_func
return handler_func
def domain_event_handler(self, handler_func):
"""Event handler decorator"""
event_cls, _ = get_function_arguments(handler_func)
self.event_handlers[event_cls].add(handler_func)
return handler_func
def import_from(self, module_name):
importlib.import_module(module_name)
def __repr__(self):
return f"<{self.name} v{self.version} {object.__repr__(self)}>"
class Application(ApplicationModule):
def __init__(self, name=__name__, version=1.0, dependency_provider=None, **kwargs):
super().__init__(name, version)
self.dependency_provider = dependency_provider or DependencyProvider(**kwargs)
self._transaction_middlewares = []
self._on_enter_transaction_context = lambda ctx: None
self._on_exit_transaction_context = lambda ctx, exc_type, exc_val, exc_tb: None
self._modules = set([self])
def include_module(self, a_module):
assert isinstance(
a_module, ApplicationModule
), "Can only include ApplicationModule instances"
self._modules.add(a_module)
def on_enter_transaction_context(self, func):
self._on_enter_transaction_context = func
return func
def on_exit_transaction_context(self, func):
self._on_exit_transaction_context = func
return func
def transaction_middleware(self, middleware_func):
"""Middleware for processing transaction boundaries (i.e. running a command or query)"""
self._transaction_middlewares.insert(0, middleware_func)
return middleware_func
def get_query_handler(self, query):
query_cls = type(query)
for app_module in self._modules:
handler_func = app_module.query_handlers.get(query_cls)
if handler_func:
return handler_func
raise Exception(f"No query handler found for command {query_cls}")
def get_command_handler(self, command):
command_cls = type(command)
for app_module in self._modules:
handler_func = app_module.command_handlers.get(command_cls)
if handler_func:
return handler_func
raise Exception(f"No command handler found for command {command_cls}")
def get_event_handlers(self, event):
event_cls = type(event)
event_handlers = []
for app_module in self._modules:
event_handlers.extend(app_module.event_handlers.get(event_cls, []))
return event_handlers
def transaction_context(self, **dependencies):
return TransactionContext(self, **dependencies)
def execute_command(self, command, **dependencies):
with self.transaction_context(**dependencies) as ctx:
return ctx.execute(command)
def execute_query(self, query, **dependencies):
with self.transaction_context(**dependencies) as ctx:
return ctx.execute_query(query)