Skip to main content

CQRS Pattern (@xndrjs/cqrs)

Command Query Responsibility Segregation (CQRS) separates commands (mutations) from queries (reads) for better scalability and maintainability.

Installation​

npm install @xndrjs/cqrs

Overview​

The @xndrjs/cqrs package provides three main buses:

  • CommandBus - Handles commands (mutations/actions)
  • QueryBus - Handles queries (reads)
  • EventBus - Publishes and subscribes to domain events

Key Concepts​

Commands​

Commands represent actions that change state. They don't return values, only success/error.

class CreateTodoCommand extends Command<"CreateTodo", { text: string }> {
  constructor(payload: { text: string }) {
    super("CreateTodo", payload);
  }
}

Queries​

Queries represent read operations. They return results.

class GetTodosQuery extends Query<"GetTodos", {}, Todo[]> {
  constructor() {
    super("GetTodos", {});
  }
}

Events​

Events represent something that happened in the domain.

class TodoCreatedEvent extends DomainEvent<"TodoCreated", { id: string; text: string }> {
  constructor(payload: { id: string; text: string }) {
    super("TodoCreated", payload);
  }
}

Next Steps​