This repository offers a message bus system tailored for integration with python-dependency-injector . It efficiently manages command and query dispatching and supports dependency injection, enhancing application decoupling, organization, and maintainability.

The source code is currently hosted on GitHub at: https://github.com/Retr0327/py-knot

Binary installers for the latest released version are available at the Python Package Index (PyPI).

• pip

  pip install pyknot

• poetry

  poetry add pyknot

1. Define messages:

   Create specific command or query messages by extending Command or Query classes.

   from dataclasses import dataclass
   from knot import Command
   
   ReturnType = dict[str, int]
   
   
   @dataclass(slots=True)
   class TestCommand(Command[ReturnType]):
       a: int
       b: int

2. Define handlers:

   Implement CommandHandler or QueryHandler for handling defined messages.

   from dataclasses import dataclass
   from knot import Command, CommandHandler
   
   ReturnType = dict[str, int]
   
   
   @dataclass(slots=True)
   class TestCommand(Command[ReturnType]):
       a: int
       b: int
   
   
   class TestCommandHandler(CommandHandler[TestCommand]):
       def handle(self, message: TestCommand) -> ReturnType:
           ... # do something

3. Register handlers:

   Register handlers to MessageBus by using register_handler method.

   from dataclasses import dataclass
   from knot import (
        Command,
        CommandHandler,
        MessageBus,
        register_handlers,
    )
   
   ReturnType = dict[str, int]
   
   
   @dataclass(slots=True)
   class TestCommand(Command[ReturnType]):
       a: int
       b: int
   
   
   class TestCommandHandler(CommandHandler[TestCommand]):
       def handle(self, message: TestCommand) -> ReturnType:
           ... # do something
   
   
   messages = register_handlers((TestCommandHandler,))
   message_bus = MessageBus(messages=messages)

4. Dispatch Messages:

   Utilize MessageBus to dispatch messages within your application

   from dataclasses import dataclass
   from knot import (
        Command,
        CommandHandler,
        MessageBus,
        register_handlers,
    )
   
   ReturnType = dict[str, int]
   
   
   @dataclass(slots=True)
   class TestCommand(Command[ReturnType]):
      a: int
      b: int
   
   
   class TestCommandHandler(CommandHandler[TestCommand]):
      def handle(self, message: TestCommand) -> ReturnType:
          ... # do something
   
   
   messages = register_handlers((TestCommandHandler,))
   message_bus = MessageBus(messages=messages)
   message_bus.dispatch(TestCommand(a=1, b=2))

please make sure you have installed python-dependency-injector

1. Set Up Dependency Injection Container

   from dataclasses import dataclass
   from dependency_injector import (
       containers,
       providers,
       )
   
   from knot import (
       Command,
       CommandHandler,
       MessageBus,
       register_handlers,
   )
   from knot.plugins.di import handlers_to_factories
   
   ReturnType = dict[str, int]
   
   
   @dataclass(slots=True)
   class TestCommand(Command[ReturnType]):
       a: int
       b: int
   
   
   class TestCommandHandler(CommandHandler[TestCommand]):
       def handle(self, message: TestCommand) -> ReturnType:
           return message.as_dict()
   
   
   messages = register_handlers((TestCommandHandler,))
   
   
   class MessageBusContainer(containers.DeclarativeContainer):
       message_bus = providers.Singleton(
           MessageBus,
           messages=providers.Dict(handlers_to_factories(messages)),
       )

   In this container, you'll manage your dependencies, including the message bus. The key function here is handlers_to_factories, transforming the handlers into factory providers that are compatible with the dependency injection framework.

2. Wire Dependencies and Dispatch Command

   Wire the dependencies and dispatch commands through the message bus, and inject the message bus to whereever you need it.

   from dependency_injector.wiring import inject, Provide
   
   @inject
   def test(
       message_bus: MessageBus = Provide["message_bus"],
   ):
       return message_bus.dispatch(TestCommand(a=1, b=2))
   
   if __name__ == "__main__":
       container = MessageBusContainer()
       container.wire(modules=[__name__])
       test()

please ensure that your application is already configured to work with Celery

py-knot can be extended to work seamlessly with Celery, enabling the dispatching of messages to a task queue. This extension is particularly useful for applications that require asynchronous processing or distributed task execution.

1. Extend MessageBus for Celery Integration

   Change:

   from knot import MessageBus

   to

   from knot.plugins.celery import MessageBus

2. Wire queue_dispatcher_module to the DI Container

   Wiring queue_dispatcher_module to the DI container makes the dispatch_queue method accessible as a dependency.

   from dataclasses import dataclass
   
   from dependency_injector import (
       containers,
       providers,
   )
   from dependency_injector.wiring import (
       Provide,
       inject,
   )
   
   from knot import (
       Command,
       CommandHandler,
       register_handlers,
   )
   from knot.plugins.celery import (
       MessageBus,
       queue_dispatcher_module,
   )
   from knot.plugins.di import handlers_to_factories
   
   ReturnType = dict[str, int]
   
   
   @dataclass(slots=True)
   class TestCommand(Command[ReturnType]):
       a: int
       b: int
   
   
   class TestCommandHandler(CommandHandler[TestCommand]):
       def handle(self, message: TestCommand) -> ReturnType:
           return message.as_dict()
   
   
   messages = register_handlers((TestCommandHandler,))
   
   
   class MessageBusContainer(containers.DeclarativeContainer):
       message_bus = providers.Singleton(
           MessageBus,
           messages=providers.Dict(handlers_to_factories(messages)),
       )
   
   
   @inject
   def test(
       message_bus: MessageBus = Provide["message_bus"],
   ):
       return message_bus.dispatch_queue(TestCommand(a="a", b="b"))
   
   
   if __name__ == "__main__":
       container = MessageBusContainer()
       container.wire(modules=[__name__, queue_dispatcher_module])
       test()

If you have any suggestion or question, please do not hesitate to email me at [email protected].