Node-Casbin Watcher based on MongoDB Change Streams

For more information about MongoDB Change Streams, look here.

More information about Casbin Watchers, look here.

Installation

```shell script

NPM

npm install --save @casbin/mongo-changestream-watcher

Yarn

yarn add @casbin/mongo-changestream-watcher

## Simple Example using Mongoose Adapter

```typescript
import { MongoChangeStreamWatcher } from '@casbin/mongo-changestream-watcher';
import { newEnforcer } from 'casbin';

// Initialize the watcher by connecting to a replica set.
const watcher = await MongoChangeStreamWatcher.newWatcher('mongodb://localhost:27001,localhost:27002/casbin?replicaSet=rs0', {collectionName: 'casbin_rule'});
const adapter = await MongooseAdapter.newAdapter('mongodb://localhost:27001,localhost:27002/casbin?replicaSet=rs0');
const enforcer = await newEnforcer('test/fixtures/basic_model.conf', adapter);

// Initialize the enforcer.
const enforcer = await newEnforcer('examples/authz_model.conf', 'examples/authz_policy.csv');

enforcer.setWatcher(watcher);

// By default, the watcher's callback is automatically set to the
// enforcer's loadPolicy() in the setWatcher() call.
// We can change it by explicitly setting a callback.
watcher.setUpdateCallback(() => console.log('Casbin need update'));

Notes

This watcher does not operate with update-calls typically found in other watchers. Mongo Change Stream directly reacts to changes in the database collection, and therefore all other watchers listening to the same stream will be automatically notified when changes do occur. However, this means that watcher also gets notified by its own changes.