⏳ [Subscription]: Returning an array of entities that match with filter criteria from @Args for Subscription resolvers

[Mingyang-Li]

Hello friends, I'm looking for a way to implement Subscription resolvers that return an array of entiries which match the filter criteria from @Args() passed in

I haven't found any issues nor PR related to this feature.

Originally submitted a similar same issue (with LOTS of details) for NestJS implementation in their repo, but sadly they're not implementing it in the forseable future.

Yet, I need to figure out a way to do this.

Any help would be appreciated:)

[MichalLytek]

@Subscription decorator has a filter argument where you can pass your function that filters payloads from pubsub and decide if you want to trigger response to client from subscription or not for that event.

Is that something you're describing? I'm not sure what kind of filtering you want.

[Mingyang-Li]

hi @MichalLytek, I was aware of the filter argument from @Subscription decorator. However, I doubt it if this feature alone can help me build a subscription resolver that allows me to do something like this:

subscription {
  subscribeUsers (
    where: {
      id: { _eq: 'djfdf2387b' },
      createdAt: { _gte: '2022-08-31' }
    },
    orderBy: {
      id: Asc,
      amount: Desc
      createdAt: Asc
    },
    skip: 4,
    take: 6,
  ) {
     id
     firstName
     paymentsCreated {
       id
       amount
       currency
     }
  }
}

Which, returns me an array of User entities that match the filters from arguments within subscribeUsers

[MichalLytek]

filter allows preventing triggering subscription on pubsub event. You can also do Array.prototype.filter in your resolver to filter the returned array.

Based on your example in NestJS repo, you should setup pubsub to trigger topic when something changes in observed table and then in the subscription resolver, just fetch the data from db using args as sql where conditions. Does it solves your problem?

[Mingyang-Li]

Hmmm, so did you mean I need to query the updated entities on create and update instead of within subsciption resolver?

For e.g,:

import { Args, Mutation, Query, Resolver, Subscription } from '@nestjs/graphql';
import { PubSub } from 'graphql-subscriptions';
import { CreatePaymentArgs } from 'src/payment/dtos/CreatePaymentArgs';
import { UpdatePaymentArgs } from 'src/payment/dtos/UpdatePaymentArgs';
import { Payment } from './dtos/Payment';
import { PaymentFindManyArgs } from './dtos/PaymentFindManyArgs';
import { PaymentService } from './payment.service';

@Resolver(() => Payment)
export class PaymentResolver {
  constructor(private paymentService: PaymentService, private pubSub: PubSub) {}

  @Mutation(() => Payment)
  public async createPayment(
    @Args() args: CreatePaymentArgs,
  ): Promise<Payment> {
    const newPayment = await this.paymentService.create(args);
    if (newPayment) {
      const payments = this.paymentService.findMany(args);
      this.pubSub.publish('paymentsUpdated', payments);
    };
    return newPayment;
  }

  @Mutation(() => Payment)
  public async updatePayment(
    @Args() args: UpdatePaymentArgs,
  ): Promise<Payment> {
    const updatedPayment = await this.paymentService.update(args);
    if (updatedPayment) {
      const payments = this.paymentService.findMany(args);
      this.pubSub.publish('paymentsUpdated', payments);
    };
    return updatedPayment;
  }

  @Query(() => [Payment])
  public async payments(@Args() args: PaymentFindManyArgs): Promise<Payment[]> {
    return this.paymentService.findMany(args);
  }

  @Subscription(() => [Payment])
  public async subscribePayments(@Args() args: PaymentFindManyArgs) {
    return this.pubSub.asyncIterator('paymentsUpdated');
  }
}

I updated my updatePayment and createPayment resolvers, to get PubSub to publish an array of Payments on update or create, do you think that's a feasible solution?