🚌 bus — Lightweight CQRS Library for Rust

bus is a modular, async-first CQRS library for Rust that helps you structure your application around clear boundaries: Commands, Queries, and Events. It supports both in-memory and database-backed event processing, middleware pipelines, and graceful shutdown — all with minimal boilerplate.

🧠 What Problems Does bus Solve?

• ❌ Tightly coupled business logic and infrastructure
• ❌ Scattered side effects and background jobs
• ❌ No clear separation between commands, queries, and events
• ❌ Manual registration of handlers and middleware

✅ bus introduces a clean, extensible architecture for:

• 🧱 Structuring your domain logic with CQRS
• 🔁 Handling commands and queries with type-safe handlers
• 📬 Publishing events (in-memory or persisted)
• 🧩 Composing middleware pipelines for logging, validation, metrics, etc.
• 🧵 Running background workers for database-backed events

🧭 What is CQRS?

CQRS stands for Command Query Responsibility Segregation — a pattern that separates:

• Commands — operations that change state (e.g. CreateUser)
• Queries — operations that return data (e.g. GetUserById)
• Events — notifications that something happened (e.g. UserCreated)

This separation improves clarity, testability, and scalability.

🧱 Core Concepts

🔨 Command

A command represents an intention to change state. It is handled by a single handler and returns a result.

📖 Read more → command.md

🔍 Query

A query retrieves data without modifying state. It is also handled by a single handler.

📖 Read more → query.md

📣 Event

An event represents something that has already happened. It can be:

In-memory — handled immediately during bus::publish(...)

Database-backed — persisted and processed asynchronously by background workers

• 📖 Read more → event.md
• 📖 Database-backed events → event_database_sea_orm.md

🧩 Middleware Pipelines

You can wrap handlers with composable pipelines for:

• Logging
• Validation
• Metrics
• Tracing
• Retry instrumentation

Supported for:

• In-memory events → event_pipeline.md
• Database-backed events → event_database_pipeline.md
• Requests (commands/queries) → request_pipeline.md

⚙️ Installation

Add bus to your Cargo.toml:

[dependencies]
bus = { package = "rust_bus", version = "" }
ctor = "0.4" # Required for automatic handler & pipeline registration

Why ctor?

bus uses the ctor crate to automatically register handlers and pipelines at startup. Without it, nothing will be wired up.

📦 Migrations for Database Events

If you're using database-backed events with SeaORM, you must apply the required database migrations before running workers.

All required migrations are located in the root of the repository under the migration/ directory:

/migration
├── 2023_..._create_bus_events_table.sql
├── 2023_..._create_bus_events_archive.sql
└── ...

migration

You can apply them using your preferred migration tool (e.g. SeaORM CLI, refinery, sqlx-cli, or manually via psql/MySQL client).

🚀 Getting Started

1. Define your command, query, or event
2. Implement the corresponding handler trait
3. Register it using a macro (e.g. #bus::registry::BusCommandHandler)
4. Optionally define pipelines for cross-cutting concerns
5. Use bus::send(...) or bus::publish(...) to dispatch

🧠 Design Philosophy

• ✅ Explicit over implicit
• ✅ Async-first
• ✅ Minimal boilerplate
• ✅ Composable middleware
• ✅ Type-safe boundaries

📚 Documentation Index

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