Node sagas

This is a repository for the node-sagas package. node-sagas is a convenient library for managing data consistency in a microservice architecture. It helps create distributed transaction across services.

Why Sagas?

A distinctive characteristic of the microservice architecture is that in order to ensure loose coupling each service’s data is private. Unlike in a monolithic application, you no longer have a single database that any module of the application can update. As a result, one of the key challenges that you will face is maintaining data consistency across services.

Please read more about saga pattern.

Installing / Getting started

This module is installed via npm::

npm i --save node-sagas 

Example

This package provides you with main classes for creating sagas. The first main class is SagaBuilder.

  import { SagaBuilder } from 'node-sagas';
  
  const sagaBuilder = new SagaBuilder<CreateOrderSagaParams>();
  const saga = sagaBuilder
    .step('Create order')
    .invoke((params: CreateOrderSagaParams) => {
      // create order logic
    })
    .withCompensation((params: CreateOrderSagaParams) => {
      // reject order logic
    })
    .step('Reserve credit')
    .invoke((params: CreateOrderSagaParams) => {
      // reserve credit
    })
    .step('Approve order')
    .invoke((params: CreateOrderSagaParams) => {
      // approve order
    })
    .build();

    const params = new CreateOrderSagaParams();

    try {
      return await saga.execute(params);
    } catch (e) {
      if (e instanceof SagaExecutionFailed) {
        // Throws, when invocation flow was failed, but compensation has been completed
      }
      if (e instanceof SagaCompensationFailed) {
        // Throws, when compensation flow was failed
      }
    }

A step could be defined using step() method, for each step you can set an action for a positive case with invoke() method. Also for each step, you can define compensation action with withCompensation() method.

SagaBuilder class use generic class for the handler's params:

export class CreateOrderSagaParams {
  private orderId: number;
  private customerId: number;

  public getOrderId() {
    return this.orderId;
  }

  public setOrderId(orderId) {
    this.orderId = orderId;
  }

  public getCustomerId() {
    return this.customerId;
  }

  public setCustomerId(customerId) {
    this.customerId = customerId;
  }
}

That class represents scope with params between the steps. Also, an instance of that class will be returned after the saga success execution.

Links

The article on Medium with a practical example will be prepared soon.

Licensing

The code in this project is licensed under MIT license.