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December 25, 2021 18:29
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Type safe MongoDB change stream
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import { EventEmitter } from 'events'; | |
import { getInstance } from './core-util/mongo'; | |
import { ChangeEvent, ChangeEventCR, ChangeEventDelete, ChangeEventUpdate, ChangeStream, ObjectId } from 'mongodb'; | |
type ChangeListenerFunction<T> = (payload: T) => void; | |
interface User { | |
address: { | |
city: string | |
country: string | |
} | |
person: { | |
firstName: string | |
lastName: string | |
} | |
} | |
export class ChangeListener<TModel extends object> { | |
private emitter: EventEmitter; | |
private collection: string; | |
private changeStream: ChangeStream<TModel> | null = null; | |
constructor(collection: string) { | |
this.emitter = new EventEmitter(); | |
this.collection = collection; | |
this.startWatching(); | |
} | |
on(name: 'created', fn: ChangeListenerFunction<TModel>): void; | |
on(name: 'updated', fn: ChangeListenerFunction<TModel>): void; | |
on(name: 'deleted', fn: ChangeListenerFunction<ObjectId>): void; | |
on<TKey extends string & keyof TModel>(name: `${TKey}Changed`, fn: ChangeListenerFunction<TModel[TKey] | null>): void; | |
on(name: string, fn: ChangeListenerFunction<any>): void { | |
this.emitter.on(name, fn); | |
} | |
once(name: 'created', fn: ChangeListenerFunction<TModel>): void; | |
once(name: 'updated', fn: ChangeListenerFunction<TModel>): void; | |
once(name: 'deleted', fn: ChangeListenerFunction<ObjectId>): void; | |
once<TKey extends string & keyof TModel>(name: `${TKey}Changed`, fn: ChangeListenerFunction<TModel[TKey] | null>): void; | |
once(name: string, fn: ChangeListenerFunction<any>): void { | |
this.emitter.once(name, fn); | |
} | |
off(name: 'created', fn: ChangeListenerFunction<TModel>): void; | |
off(name: 'updated', fn: ChangeListenerFunction<TModel>): void; | |
off(name: 'deleted', fn: ChangeListenerFunction<ObjectId>): void; | |
off<TKey extends string & keyof TModel>(name: `${TKey}Changed`, fn: ChangeListenerFunction<TModel[TKey] | null>): void; | |
off(name: string, fn: ChangeListenerFunction<any>): void { | |
this.emitter.off(name, fn); | |
} | |
emit(name: 'created', payload: TModel): void; | |
emit(name: 'updated', payload: TModel): void; | |
emit(name: 'deleted', payload: ObjectId): void; | |
emit<TKey extends string & keyof TModel>(name: `${TKey}Changed`, payload: TModel[TKey] | null): void; | |
emit(name: string, payload: unknown): void { | |
this.emitter.emit(name, payload); | |
} | |
private async startWatching() { | |
if (this.changeStream) return; | |
try { | |
const db = await getInstance(); | |
this.changeStream = db.collection(this.collection).watch(null, { fullDocument: 'updateLookup' }); | |
this.changeStream?.on('change', this.onChange); | |
} catch (error) { | |
console.log(error); | |
this.changeStream?.close(); | |
} | |
} | |
private onChange(event: ChangeEvent<TModel>) { | |
switch (event.operationType) { | |
case 'insert': | |
this.onCreate(event); | |
break; | |
case 'update': | |
this.onUpdate(event); | |
break; | |
case 'delete': | |
this.onDelete(event); | |
break; | |
default: | |
console.log(`Operation not supported: ${event.operationType}`); | |
break; | |
} | |
} | |
private onCreate(event: ChangeEventCR<TModel>) { | |
console.log(`Created a document in the ${this.collection} collection with ID ${event.documentKey._id}`); | |
this.emit('created', event.fullDocument!); | |
} | |
private onUpdate(event: ChangeEventUpdate<TModel>) { | |
console.log(`Updated a document in the ${this.collection} collection with ID ${event.documentKey._id}`); | |
this.emit('updated', event.fullDocument!); | |
Object | |
.entries(event.updateDescription.updatedFields) | |
.forEach(([key, value]) => this.emit(`${key}Changed` as any, value)); | |
event.updateDescription.removedFields | |
.forEach((key) => this.emit(`${key}Changed` as any, null)); | |
} | |
private onDelete(event: ChangeEventDelete<TModel>) { | |
console.log(`Deleted a document in the ${this.collection} collection with ID ${event.documentKey._id}`); | |
this.emit('deleted', event.documentKey._id); | |
} | |
} | |
const userEvents = new ChangeListener<User>('users'); | |
userEvents.on('deleted', (id) => { | |
}); | |
userEvents.on('created', (user) => { | |
}); | |
userEvents.on('personChanged', (person) => { | |
}); |
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