[NestJS] NestJS DataLoader

NestJS Data Loader

• N+1 문제를 해결하기 위해 사용

Installation

npm i nestjs-dataloader --save

사용 방법

1. DataLoader 생성

• 첫 번째 제네릭은 DB의 ID 타입
• 두 번째 제네릭은 return될 타입

import { Injectable } from '@nestjs/common';
import * as DataLoader from 'dataloader';
import { NestDataLoader } from 'nestjs-dataloader';
import { RateplanService } from '../service/rateplan.service';
import { RateplanObjectType } from '@/graphql/rateplan/type/rateplan.object-type';

@Injectable()
export class RateplanChildLoader implements NestDataLoader<number, RateplanObjectType[]> {
  constructor(private readonly rateplanService: RateplanService) {}

  generateDataLoader(): DataLoader<number, RateplanObjectType[]> {
    return new DataLoader<number, RateplanObjectType[]>(async (keys) => {
      const childRateplans: RateplanObjectType[] = await this.rateplanService.getChildRateplans(<number[]>keys);
      return keys.map((key) => childRateplans.filter((childRateplan) => childRateplan.parentId === key));
    });
  }
}

2. DataLoader를 모듈에 provider로 추가

import { Module } from '@nestjs/common';

import { RateplanResolver } from './resolver/rateplan.resolver';
import { RateplanService } from './service/rateplan.service';
import { CommonRateplanService, CommonRateplanTemplateService } from '@/services';
import { RateplanSubResolver } from './resolver/rateplan.sub-resolver';
import { RateplanInformationLoader } from './resolver/loader/rateplan-information.loader';
import { DataLoaderInterceptor } from 'nestjs-dataloader';
import { APP_INTERCEPTOR } from '@nestjs/core';
import { RateplanChildLoader } from './resolver/loader/rateplan-child.loader';
@Module({
  exports: [RateplanService],
  providers: [
    // Resolver
    RateplanResolver,
    RateplanSubResolver,

    //Service
    RateplanService,
    CommonRateplanService,
    CommonRateplanTemplateService,

    // DataLoader
    RateplanInformationLoader,
    RateplanChildLoader,
    {
      provide: APP_INTERCEPTOR,
      useClass: DataLoaderInterceptor,
    },
  ],
})
export class RateplanModule {}

3. Resolver에서 DataLoader 사용

• @Loader Decorator의 매개변수가 메소드에 주입하고자 하는 DataLoader class
• 주입된 DataLoader 메소드로 대량 검색 및 캐싱을 처리

import { Resolver, ResolveField, Parent } from '@nestjs/graphql';
import { RateplanObjectType } from '../type/rateplan.object-type';
import { RateplanService } from '../service/rateplan.service';
import { RateplanInformationObjectType } from '../type/rateplan-information.object.type';
import { RateplanInformationLoader } from './loader/rateplan-information.loader';
import * as DataLoader from 'dataloader';
import { Loader } from 'nestjs-dataloader';
import { RateplanChildLoader } from './loader/rateplan-child.loader';

@Resolver((of) => RateplanObjectType)
export class RateplanSubResolver {
  constructor(private readonly rateplanService: RateplanService) {}

  @ResolveField((returns) => RateplanInformationObjectType)
  public async rateplanInformations(
    @Parent() rateplan: RateplanObjectType,
    @Loader(RateplanInformationLoader.name)
    rateplanLoader: DataLoader<RateplanObjectType['id'], RateplanInformationObjectType>,
  ): Promise {
     return rateplanLoader.load(rateplan.id);
    }
  }

Array로 리턴하는 Case

import { Injectable } from '@nestjs/common';
import * as DataLoader from 'dataloader';
import { NestDataLoader } from 'nestjs-dataloader';
import { RateplanService } from '../../service/rateplan.service';
import { RateplanInformationObjectType } from '../../type/rateplan-information.object.type';

@Injectable()
export class RateplanInformationLoader implements NestDataLoader<number, RateplanInformationObjectType[]> {
  constructor(private readonly rateplanService: RateplanService) {}

  generateDataLoader(): DataLoader<number, RateplanInformationObjectType[]> {
    return new DataLoader<number, RateplanInformationObjectType[]>(async (keys) => {
      const rateplanInformations: RateplanInformationObjectType[] = await this.rateplanService.getRateplanInformations(
        <number[]>keys,
      );
      return keys.map((key) =>
        rateplanInformations.filter((rateplanInformation) => rateplanInformation.rateplanId === key),
      );
    });
  }
}

import { Resolver, ResolveField, Parent } from '@nestjs/graphql';
import { RateplanObjectType } from '../type/rateplan.object-type';
import { RateplanService } from '../service/rateplan.service';
import { RateplanInformationObjectType } from '../type/rateplan-information.object.type';
import { RateplanInformationLoader } from './loader/rateplan-information.loader';
import * as DataLoader from 'dataloader';
import { Loader } from 'nestjs-dataloader';
import { RateplanChildLoader } from './loader/rateplan-child.loader';

@Resolver((of) => RateplanObjectType)
export class RateplanSubResolver {
  constructor(private readonly rateplanService: RateplanService) {}

  @ResolveField((returns) => [RateplanInformationObjectType])
  public async rateplanInformations(
    @Parent() rateplan: RateplanObjectType,
    @Loader(RateplanInformationLoader.name)
    rateplanLoader: DataLoader<RateplanObjectType['id'], RateplanInformationObjectType[]>,
  ): Promise<RateplanInformationObjectType[]> {
    return rateplanLoader.load(rateplan.id);
  }
}

 

www.npmjs.com/package/nestjs-dataloader

nestjs-dataloader