lexigram-events

Event Sourcing and CQRS engine for Lexigram Framework — domain events, aggregates, and projections.

Overview

CQRS, Event Sourcing, and messaging for Lexigram — command bus, event bus, event store, sagas, and projections. Provides a full CQRS stack: a typed command bus, an in-process pub/sub event bus, an append-only event store (PostgreSQL, SQLite, MongoDB, in-memory), saga orchestration, projections, and outbox processing.

Use EventsModule.configure() to register the event system and dispatch commands or subscribe to events via decorators.

Full documentation: docs.lexigram.dev

Install

uv add lexigram-events
# Optional extras
uv add "lexigram-events[postgres,sqlite,mongo]"

Quick Start

from lexigram import Application
from lexigram.di.module import Module, module
from lexigram.events import EventsModule, EventsConfig

@module(imports=[EventsModule.configure()])
class AppModule(Module):
    pass

async def main():
    async with Application.boot(modules=[AppModule]) as app:
        # your event sourcing code
        ...

if __name__ == "__main__":
    import asyncio
    asyncio.run(main())

Configuration

Zero-config usage: Call EventsModule.configure() with no arguments to use defaults (in-memory event store and bus).

Option 1 — YAML file

# application.yaml
events:
  event_store_backend: postgres
  postgres:
    dsn: "${DATABASE_URL}"

Option 2 — Profiles + Environment Variables (recommended)

export LEX_EVENTS__EVENT_STORE_BACKEND=postgres
export LEX_EVENTS__POSTGRES__DSN="postgresql://user:pass@host/db"

Option 3 — Python

from lexigram.events import EventsConfig, EventsModule, PostgresEventStoreConfig
from lexigram.events.types import EventStoreBackend

config = EventsConfig(
    event_store_backend=EventStoreBackend.POSTGRES,
    postgres=PostgresEventStoreConfig(dsn="${DATABASE_URL}"),
)
EventsModule.configure(config)

Config reference

Module Factory Methods

WebSocket Event Streaming

EventWebSocketEndpoint streams every event published to a StreamDispatcher to connected WebSocket clients in real time.

Security: the endpoint does not authenticate connections by default. With no authorize callback, any client that can reach the endpoint receives a live, unauthenticated stream of all dispatched events — potentially business-sensitive or PII-bearing. Always pass an authorize callback in production:

from lexigram.events.streaming import EventWebSocketEndpoint, StreamDispatcher


def authorize(scope: dict) -> bool:
    headers = dict(scope.get("headers") or [])
    return headers.get(b"authorization") == b"Bearer secret"


dispatcher = StreamDispatcher()
ws_app = EventWebSocketEndpoint(dispatcher, authorize=authorize)

The callback receives the ASGI connection scope (headers, query string, client) and may be synchronous or asynchronous; returning a falsy value rejects the connection with a 4401 close before the handshake is accepted.

Key Features

• CommandBus — Typed async command dispatch with middleware
• EventBus — In-process pub/sub with dead-letter handling
• EventStore — Append-only store (PostgreSQL, SQLite, MongoDB, in-memory)
• Saga — Long-running process orchestration with compensating transactions
• Projection — Read-model rebuilding from event streams
• Outbox — Reliable event delivery via transactional outbox pattern
• Schema migration — Versioned event schema evolution

Testing

async with Application.boot(modules=[EventsModule.stub()]) as app:
    # your test code
    ...

Key Source Files