Ensuring Sequelize Hooks Always Get Run
Intro
In "Decoupling Logic with Domain Events [Guide] - Domain-Driven Design w/ TypeScript", we use Sequelize Hooks to decouple business logic, allowing the system to respond to events in a fashion similar to the Observer Pattern.
Sequelize hooks are places we can write callbacks that get invoked at key points in time like afterCreate, afterDestroy, afterUpdate, and more.
import models from "../models"
import { DomainEvents } from "../../../core/domain/events/DomainEvents"
import { UniqueEntityID } from "../../../core/domain/UniqueEntityID"
const dispatchEventsCallback = (model: any, primaryKeyField: string) => {
const aggregateId = new UniqueEntityID(model[primaryKeyField])
DomainEvents.dispatchEventsForAggregate(aggregateId)
}
(async function createHooksForAggregateRoots() {
const { User } = models
User.addHook("afterCreate", (m: any) => dispatchEventsCallback(m, "user_id"))
User.addHook("afterDestroy", (m: any) => dispatchEventsCallback(m, "user_id"))
User.addHook("afterUpdate", (m: any) => dispatchEventsCallback(m, "user_id"))
User.addHook("afterSave", (m: any) => dispatchEventsCallback(m, "user_id"))
User.addHook("afterUpsert", (m: any) => dispatchEventsCallback(m, "user_id"))
})()In Domain-Driven Design, after a transaction completes, we want to execute domain event handlers in order to decide whether we should invoke any follow up commands or not.
import { UserCreated } from "../../users/domain/events/userCreated"
import { IHandle } from "../../../shared/domain/events/IHandle"
import { CreateMember } from "../useCases/members/createMember/CreateMember"
import { DomainEvents } from "../../../shared/domain/events/DomainEvents"
export class AfterUserCreated implements IHandle<UserCreated> {
private createMember: CreateMember
constructor(createMember: CreateMember) {
this.setupSubscriptions()
this.createMember = createMember
}
setupSubscriptions(): void {
// Register to the domain event
DomainEvents.register(this.onUserCreated.bind(this), UserCreated.name) }
private async onUserCreated(event: UserCreated): Promise<void> { const { user } = event
try {
await this.createMember.execute({ userId: user.userId.id.toString() })
console.log(
`[AfterUserCreated]: Successfully executed CreateMember use case AfterUserCreated`
)
} catch (err) {
console.log(
`[AfterUserCreated]: Failed to execute CreateMember use case AfterUserCreated.`
)
}
}
}In the Sequelize Repository, where we deal with persistence logic, I have noticed that the hook callbacks do not get called if no new rows were created and no columns were changed.
In the save method of a repository, you'll find code where we rely on a mapper to convert the domain object to the format necessary for Sequelize to save it. You'll also find code that determines if we're doing a create or an update based on the domain object's existence.
export class SequelizePostRepo implements PostRepo {
...
public async save (post: Post): Promise<void> {
const PostModel = this.models.Post;
const exists = await this.exists(post.postId);
const isNewPost = !exists;
const rawSequelizePost = await PostMap.toPersistence(post);
if (isNewPost) {
try {
await PostModel.create(rawSequelizePost);
await this.saveComments(post.comments);
await this.savePostVotes(post.getVotes());
} catch (err) {
await this.delete(post.postId);
throw new Error(err.toString())
}
} else {
await this.saveComments(post.comments);
await this.savePostVotes(post.getVotes());
// Persist the post model to the database await PostModel.update(rawSequelizePost, { where: { post_id: post.postId.id.toString() } }); }
}
}In the highlighted lines, I expect the afterUpdate hook to get called, though it will not in scenarios where there were no are differences.
To fix this, Sequelize's update method's second parameter configuration object allows you to pass in hooks: true.
await PostModel.update(rawSequelizePost, {
where: { post_id: post.postId.id.toString() }
// Be sure to include this to call hooks regardless
// of anything changed or not.
hooks: true,});Doing this will ensure that the hooks get run everytime.
Discussion
Liked this? Sing it loud and proud 👨🎤.
Stay in touch!
We're just getting started 🔥 Interested in how to write professional JavaScript and TypeScript? Join 5000+ other developers learning about Domain-Driven Design and Enterprise Node.js. I won't spam ya. 🖖 Unsubscribe anytime.
View more in Sequelize
You may also enjoy...
A few more related articles
Trending Content
Software Design and Architecture is pretty much its own field of study within the realm of computing, like DevOps or UX Design. Here's a map describing the breadth of software design and architecture, from clean code to microkernels.
Learn how to use DDD and object-oriented programming concepts to model complex Node.js backends.
Want to be notified when new content comes out?
Join 5000+ other developers learning about Domain-Driven Design and Enterprise Node.js.
I won't spam ya. 🖖 Unsubscribe anytime.
• Open sourced on
• Deployed on
0 Comments
Be the first to leave a comment