NestJS dataloader simplifies adding graphql/dataloader to your NestJS project. DataLoader aims to solve the common N+1 loading problem.
Install with yarn
yarn add nestjs-dataloaderInstall with npm
npm install --save nestjs-dataloaderWe start by implementing the NestDataLoader interface. This tells DataLoader how to load our objects.
import * as DataLoader from 'dataloader';
import { Injectable } from '@nestjs/common';
import { NestDataLoader } from 'nestjs-dataloader';
...
@Injectable()
export class AccountLoader implements NestDataLoader<string, Account> {
constructor(private readonly accountService: AccountService) { }
generateDataLoader(): DataLoader<string, Account> {
return new DataLoader<string, Account>(keys => this.accountService.findByIds(keys));
}
}The first generic of the interface is the type of ID the datastore uses. The second generic is the type of object that will be returned. In the above instance, we want DataLoader to return instances of the Account class.
For each NestDataLoader we create, we need to provide it to our module.
import { Module } from '@nestjs/common';
import { APP_INTERCEPTOR } from '@nestjs/core';
import {DataLoaderInterceptor} from 'nestjs-dataloader'
...
@Module({
providers: [
AccountResolver,
AccountLoader,
{
provide: APP_INTERCEPTOR,
useClass: DataLoaderInterceptor,
},
],
})
export class ResolversModule { }Now that we have a dataloader and our module is aware of it, we need to pass it as a parameter to an endpoint in our graphQL resolver.
import * as DataLoader from 'dataloader';
import { Loader } from 'nestjs-dataloader';
...
@Resolver(Account)
export class AccountResolver {
@Query(() => [Account])
public getAccounts(
@Args({ name: 'ids', type: () => [String] }) ids: string[],
@Loader(AccountLoader) accountLoader: DataLoader<Account['id'], Account>): Promise<Account[]> {
return accountLoader.loadMany(ids);
}
}The important thing to note is that the parameter of the @Loader decorator is the entity/class of the NestDataLoader we want to be injected to the method. The DataLoader library will handle bulk retrieval and caching of our requests. Note that the caching is stored on a per-request basis.
Pull requests are always welcome. For major changes, please open an issue first to discuss what you would like to change.
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