aiogram provides powerful mechanism for customizing event handlers via middlewares.
Middlewares in bot framework seems like Middlewares mechanism in web-frameworks (like aiohttp, fastapi, Django or etc.) with small difference - here is implemented two layers of middlewares (before and after filters).
Middleware is function that triggered on every event received from Telegram Bot API in many points on processing pipeline.
As many books and other literature in internet says:
Middleware is reusable software that leverages patterns and frameworks to bridge the gap between the functional requirements of applications and the underlying operating systems, network protocol stacks, and databases.
Middleware can modify, extend or reject processing event in many places of pipeline.
Middleware instance can be applied for every type of Telegram Event (Update, Message, etc.) in two places
- Outer scope - before processing filters (
- Inner scope - after processing filters but before handler (
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Middleware should be subclass of
from aiogram import BaseMiddleware) or any async callable
||Wrapped handler in middlewares chain|
||Incoming event (Subclass of
||Contextual data. Will be mapped to handler arguments|
Middleware should always call
await handler(event, data) to propagate event for next middleware/handler
from aiogram import BaseMiddleware from aiogram.api.types import Message class CounterMiddleware(BaseMiddleware[Message]): def __init__(self) -> None: self.counter = 0 async def __call__( self, handler: Callable[[Message, Dict[str, Any]], Awaitable[Any]], event: Message, data: Dict[str, Any] ) -> Any: self.counter += 1 data['counter'] = self.counter return await handler(event, data)
router = Router() router.message.middleware(CounterMiddleware())
@dispatcher.update.outer_middleware() async def database_transaction_middleware( handler: Callable[[Update, Dict[str, Any]], Awaitable[Any]], event: Update, data: Dict[str, Any] ) -> Any: async with database.transaction(): return await handler(event, data)
- Middlewares from outer scope will be called on every incoming event
- Middlewares from inner scope will be called only when filters pass
- Inner middlewares is always calls for
Updateevent type in due to all incoming updates going to specific event type handler through built in update handler