This library provides functional approach to CQRS (Command Query Responsibility Segregation).

NOTE: Readme is in progress

1. ✨ Getting Started
   • Prerequisites
   • Installation
2. 🚀 Usage
3. Examples

You will need:

• nodejs (>=12.13.1, not tested on older versions, but might work)

npm install functional-cqrs or yarn add functional-cqrs

Functional Cqrs splits into three basic components:

Commands are parts of applications that change it's state (for example by creating new record in database) and dispatch events respective to these actions. Commands can be executed by using CommandsBus.

Typescript

commandsBus.execute<SaveTodo>({
    name: 'SaveTodo',
    payload: todo,
  });

Javascript

commandsBus.execute({
    name: 'SaveTodo',
    payload: todo,
  });

Commands always come with two properties:

• name definies name of the command (usually named after certain domain action, ex. "SaveTodo"),
• payload Data attached to command (ex. input of entity that should be validated and saved in database)

Every command should have only one handle

Hint: Commands are usualy named in present tense

Bonus for Typescript users, you can define commands types in following way:

import { Command } from 'functional-cqrs';

export name SaveTodo = Command<'SaveTodo', Todo>;

First generic argument defines command name property, and second defines payload.

Handlers are always bound to single command, and they can return value. They can also execute queries and dispatch events

Typescript

import { commandHandler, CommandHandlerFn } from 'functional-cqrs';

export interface Context {
  connection: Connection;
}

const saveTodoHandler: CommandHandlerFn<SaveTodo, Context> = async ({
  context: {
    eventsBus,
    connection,  
  },
  command: {payload}
}) => {
  if (!payload.title) {
    throw new Error('Title is required.');
  }

  const todo = connection.save(payload);

  await eventsBus.dispatch<TodoSaved>({
    name: 'TodoSaved',
    payload: todo,
  });

  return todo;
};

export default commandHandler.asFunction<SaveTodo, Context>('SaveTodo', saveTodoHandler);

Javascript

import { commandHandler } from 'functional-cqrs';

const saveTodoHandler = async ({
  context: {
    eventsBus,
    connection,  
  },
  command: {payload}
}) => {
  if (!payload.title) {
    throw new Error('Title is required.');
  }

  const todo = connection.save(payload);

  await eventsBus.dispatch({
    name: 'TodoSaved',
    payload: todo,
  });

  return todo;
};

module.exports = commandHandler.asFunction('SaveTodo', saveTodoHandler);

Handler is a function that takes one parameter which contains "Context" (which basically contains all dependencies from your application, such as database connection and also buses related to it's name.) and query, event or command.

Hint: Remember that you always have to "decorate" your handler using "commandHandler.asFunction" or "commandHandler.asClass"