Cancel data insert inside beforeInsert event if it already exists in table - node.js

Question

There is a need to insert multiple rows in a table. I am using TypeOrm which has .save() method.
.save() method is used to insert data in bulk, and it checks for the inserting primary key ID. If they exist it updates, otherwise inserts.
I want to do the checking on some other field shortLInk. Which is not possible with .save()
So I tried to do inside beforeInsert() event, things are fine but I need to cancel the isnertions if row is find.
Is there any way to achieve it? I couldn't find anything in documentation.
I can throw an error inside beforeInsert() but it will cancel whole insertions.
async shortLinks(links: Array<string>): Promise<Array<QuickLinkDto>> {
const quickLinks: Array<QuickLinkDto> = links.map((link) => ({
actualLink: link,
}));
return this.quickLinkRepository.save(quickLinks, {});
}
#Injectable()
export class QuickLinkSubscriber
implements EntitySubscriberInterface<QuickLink>
{
constructor(
datasource: DataSource,
#InjectRepository(QuickLink)
private readonly quickLinkRepository: Repository<QuickLink>,
) {
datasource.subscribers.push(this);
}
listenTo() {
return QuickLink;
}
async beforeInsert(event: InsertEvent<QuickLink>) {
const shortLink = await getShortLink(event.entity.actualLink);
const linkExists = await this.quickLinkRepository.findOne({
where: {
shortLink,
},
});
if (linkExists) {
// Discard the insertion if the row already exists
return delete event.entity; // throws error
}
event.entity.shortLink = shortLink;
}
}

Answer 1

When you use a transaction, all the operations are atomic, meaning either all of them are executed or none of them are. you can check for the existence of the shortLink before the insert and if it exists, you can cancel the whole transaction.
async shortLinks(links: Array<string>): Promise<Array<QuickLinkDto>> {
const quickLinks: Array<QuickLinkDto> = links.map((link) => ({
actualLink: link,
}));
const queryRunner = this.quickLinkRepository.manager.connection.createQueryRunner();
try {
await queryRunner.startTransaction();
const result = await this.quickLinkRepository.save(quickLinks, {});
await queryRunner.commitTransaction();
return result;
} catch (error) {
await queryRunner.rollbackTransaction();
throw error;
} finally {
await queryRunner.release();
}
}
#Injectable()
export class QuickLinkSubscriber
implements EntitySubscriberInterface<QuickLink>
{
constructor(
datasource: DataSource,
#InjectRepository(QuickLink)
private readonly quickLinkRepository: Repository<QuickLink>,
) {
datasource.subscribers.push(this);
}
listenTo() {
return QuickLink;
}
async beforeInsert(event: InsertEvent<QuickLink>) {
const shortLink = await getShortLink(event.entity.actualLink);
const linkExists = await this.quickLinkRepository.findOne({
where: {
shortLink,
},
});
if (linkExists) {
// Discard the insertion if the row already exists
throw new Error('The short link already exists');
}
event.entity.shortLink = shortLink;
}
}