FooDataSource.js

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

class FooDataSource extends DataSource {
  constructor(dbClient) {
    super()
    this.db = dbClient
    this.loader = new DataLoader(ids => dbClient.getByIds(ids))
  }

  initialize({ context, cache } = {}) {
    this.context = context
    this.cache = cache || new InMemoryLRUCache()
  }

  didEncounterError(error) {
    throw error
  }

  cacheKey(id) {
    return `foo-${this.db.connectionURI}-${id}`
  }

  async get(id, { ttlInSeconds } = {}) {
    const cacheDoc = await cache.get(this.cacheKey(id))
    if (cacheDoc) {
      return JSON.parse(cacheDoc)
    }

    const doc = await this.loader.load(id)

    if (ttlInSeconds) {
      cache.set(this.cacheKey(id), JSON.stringify(doc), { ttl: ttlInSeconds })
    }

    return doc
  }

  async update(id, newDoc) {
    try {
      await this.db.update(id, newDoc)
      this.cache.delete(this.cacheKey(id))
    } catch (error) {
      this.didEncounterError(error)
    }
  }
}