FooDataSource-structure.js

import { DataSource } from 'apollo-datasource'
import { InMemoryLRUCache } from 'apollo-server-caching'
import DataLoader from 'dataloader'

class FooDataSource extends DataSource {
  constructor(dbClient) { ... }

  initialize({ context, cache } = {}) { ... }

  didEncounterError(error) { ... }

  cacheKey(id) { ... } 

  async get(id, { ttlInSeconds } = {}) { ... }

  async update(id, newDoc) { ... }
}