Node sagas

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

Pattern

This follows the orchestrator pattern, saga comes in different forms, this can be considered the simplest in-terms of infrastructure needed and code.
You have your main component the orchestrator which handles the flow of the distributed transaction, it kicks of the chain of steps taken in the transactions
and incase of failure it runs the compensations to return to a valid state.

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Installing / Getting started

This module is installed via npm::

``shell
npm i --save node-sagas-orchestrator
`

Main use case

This package provides you with main classes for creating sagas.
The first main class is SagaBuilder.
`typescript
import { SagaBuilder } from 'node-sagas';

const sagaBuilder = new SagaBuilder();
const saga = sagaBuilder
.setContext({
key1: true,
key2: 1
})
.step('Create order')
.withKey('CREATE_ORDER')
.invoke((sagaContextMediator: SagaContextMediator) => {
const key1 = sagaContextMediator.getContext().key1;

sagaContextMediator.setContext({
key1: false,
key2: 2
})

// create order logic
})
.withCompensation(() => {
// reject order logic
})
.step('Reserve credit')
.withKey('RESERVE_CREDIT')
.invoke(() => {
// reserve credit
})
.step('Approve order')
.withKey('APPROVE_ORDER')
.invoke(() => {
// approve order
})
.build();

try {
return await saga.execute();
} 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.

There is a state class which is shared across all steps (invocation and compensation), it's represented by the SagaContextMediator` class

| Function | Description
|------|------|
|disableStep| Disables a step by key, meaning it's invocation function won't be called|
|enableStep| Re-enables a step by key|
|isStepDisable| returns a boolean to indicate if a function is disable by key|
|getContext| returns the current context value
|setContext| overwrites the current context value

Licensing

The code in this project is licensed under MIT license.

References

- Kudos to the originial repo