cqrs

go-cqrs

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Minimal implementation of the CQRS (Command Query Responsibility Segregation) pattern for Go.

Overview

go-cqrs is a lightweight library for applying the CQRS pattern in Go applications. It provides a simple API to register and dispatch commands, register and publish events, and register and dispatch queries.

Features

• Register and Dispatch Commands (one handler per command type)
• Register and Publish Events (multiple handlers per event type)
• Register and Dispatch Queries (one handler per query, returns a result)
• Generics-based API for working with concrete types
• Safe for concurrent access (uses mutexes)

Installation

Ensure Go (>= 1.18) is installed. Add the module to your project:

go get github.com/ryanbekhen/cqrs

Or require the module directly in your go.mod:

require github.com/ryanbekhen/cqrs latest

Usage Example

See the example folder.

API (Summary)

Core types:

• type Command interface{}
• type Event interface{}
• type Query interface{}

Commands:

• RegisterCommand[C Command, R any](h CommandHandler[C, R]) — register a handler for command type C.
• DispatchCommand[C Command, R any](ctx context.Context, cmd C) (R, error) — dispatch a command to its handler.

Events:

• RegisterEvent[E Event](h EventHandler[E]) — register an event handler (multiple handlers allowed).
• Publish[E Event](ctx context.Context, e E) error — publish an event to all registered handlers.

Queries:

• RegisterQuery[Q Query, R any](h QueryHandler[Q, R]) — register a handler for query Q that returns R.
• DispatchQuery[Q Query, R any](ctx context.Context, q Q) (R, error) — execute the query and receive the result.

Common Errors

• ErrCommandHandlerNotFound — no handler registered for the dispatched command.
• ErrQueryHandlerNotFound — no handler registered for the dispatched query.

Implementation Notes

• Type-to-handler mapping is implemented with reflect.
• sync.RWMutex is used to protect handler maps for concurrent access.
• The design is intentionally minimal to stay readable and easy to extend (e.g., add middleware, tracing, or async dispatch).

Testing

Run tests with:

go test ./...

Contributing

1. Fork the repository
2. Create a new branch: git checkout -b feature-name
3. Commit your changes
4. Open a Pull Request and describe your changes

License

This project is licensed under the MIT License — see the LICENSE file.