Solve N+1 Using DataLoader

Solve N+1 Using DataLoader — GraphQL Modules documentation.

DataLoader is a generic library that aims to solve the n+1 issue in large-scale GraphQL Applications. You can read more about DataLoader.

DataLoader can be used in GraphQL Modules with an easy setup. You can use them as providers or in providers. If you want to use them as providers, you can extend the DataLoader class to benefit Dependency Injection or wrap factory functions with Inject. Scope.Operation is recommended for this usage because DataLoader works on a cache-per-request mechanism.

DataLoader as a Service

import { createModule, Scope, InjectionToken } from 'graphql-modules'
import DataLoader from 'dataloader'

export const USER_DATA_LOADER = new InjectionToken('USER_DATA_LOADER')

export const myModule = createModule({
  providers: [
    {
      provide: USER_DATA_LOADER,
      scope: Scope.Operation,
      useFactory: () => new DataLoader(keys => myBatchGetUsers(keys))
    }
  ],
  resolvers: {
    Query: {
      getUserById(root, args, context) {
        return context.injector.get(USER_DATA_LOADER).load(args.id)
      }
    }
  }
})

DataLoader in a Service

import { Injectable, Scope } from 'graphql-modules'
import DataLoader from 'dataloader'
import { MyExternalDataProvider } from './my-external-data-provider'

@Injectable({
  scope: Scope.Operation
})
export class UserProvider {
  private dataLoader = new DataLoader(keys =>
    this.myDataProvider.findUsers(keys)
  )

  constructor(private myDataProvider: MyExternalDataProvider) {}

  getUserById(userId: string) {
    return this.dataLoader.load(userId)
  }
}