GraphQL Dataloaders

import gql from 'graphql-tag';export const shopApiExtensions = gql`    extend type OrderLine {        isSubscription: Boolean!    }`

npm install dataloader

import DataLoader from 'dataloader'const LoggerCtx = 'SubscriptionDataloaderService'@Injectable({ scope: Scope.REQUEST }) // Important! Dataloaders live at the request levelexport class DataloaderService {  /**   * first level is channel identifier, second level is dataloader key   */  private loaders = new Map<string, Map<string, DataLoader<ID, any>>>()  constructor(private service: SubscriptionExtensionService) {}  getLoader(ctx: RequestContext, dataloaderKey: string) {    const token = ctx.channel?.code ?? `${ctx.channelId}`        Logger.debug(`Dataloader retrieval: ${token}, ${dataloaderKey}`, LoggerCtx)    if (!this.loaders.has(token)) {      this.loaders.set(token, new Map<string, DataLoader<ID, any>>())    }    const channelLoaders = this.loaders.get(token)!    if (!channelLoaders.get(dataloaderKey)) {      let loader: DataLoader<ID, any>      switch (dataloaderKey) {        case 'is-subscription':          loader = new DataLoader<ID, any>((ids) =>            this.batchLoadIsSubscription(ctx, ids as ID[]),          )          break        // Implement cases for your other dataloaders here        default:          throw new Error(`Unknown dataloader key ${dataloaderKey}`)      }      channelLoaders.set(dataloaderKey, loader)    }    return channelLoaders.get(dataloaderKey)!  }  private async batchLoadIsSubscription(    ctx: RequestContext,    ids: ID[],  ): Promise<Boolean[]> {    // Returns an array of ids that represent those input ids that are subscriptions    // Remember: this array can be smaller than the input array    const subscriptionIds = await this.service.whichSubscriptions(ctx, ids)    Logger.debug(`Dataloader is-subscription: ${ids}: ${subscriptionIds}`, LoggerCtx)    return ids.map((id) => subscriptionIds.includes(id)) // Important! preserve order and size of input ids array  }}

@Resolver(() => OrderLine)export class MyPluginOrderLineEntityResolver {  constructor(    private dataloaderService: DataloaderService,  ) {}  @ResolveField()  isSubscription(@Ctx() ctx: RequestContext, @Parent() parent: OrderLine) {    const loader = this.dataloaderService.getLoader(ctx, 'is-subscription')    return loader.load(parent.id)  }}