Middlewares

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Overview

Middlewares allow you to intercept and modify request processing. The python-cqrs package includes a built-in LoggingMiddleware and allows you to create custom middlewares.

LoggingMiddleware

The LoggingMiddleware is automatically added to all mediators. It logs request and response details.

# LoggingMiddleware is added automatically
mediator = bootstrap.bootstrap(
    di_container=di.Container(),
    commands_mapper=commands_mapper,
    # LoggingMiddleware is added automatically
)

Custom Middleware

Create custom middlewares by implementing the Middleware protocol:

from cqrs.middlewares import base
import time

class TimingMiddleware(base.Middleware):
    async def __call__(self, request: cqrs.Request, handle):
        start_time = time.time()
        result = await handle(request)
        elapsed = time.time() - start_time
        print(f"Request {type(request).__name__} took {elapsed:.2f}s")
        return result

class ValidationMiddleware(base.Middleware):
    async def __call__(self, request: cqrs.Request, handle):
        # Validate request
        if hasattr(request, 'validate'):
            request.validate()
        result = await handle(request)
        return result

mediator = bootstrap.bootstrap(
    di_container=di.Container(),
    commands_mapper=commands_mapper,
    middlewares=[TimingMiddleware(), ValidationMiddleware()],
)

Middleware Order

Middlewares are executed in the order they are added, with the last middleware wrapping the handler first:

Order	Middleware	Execution
1	TimingMiddleware	Executes first (outermost)
2	ValidationMiddleware	Executes second
3	Handler	Executes last (innermost)

# Execution order: TimingMiddleware -> ValidationMiddleware -> Handler
mediator = bootstrap.bootstrap(
    di_container=di.Container(),
    commands_mapper=commands_mapper,
    middlewares=[
        TimingMiddleware(),      # Executes first (outermost)
        ValidationMiddleware(),  # Executes second
    ],
)

Middleware Execution

Middlewares wrap handlers in reverse order. The first middleware in the list is the outermost wrapper, executing before all others.