graphbrainz/src/loaders.js

A GraphQL schema, Express server, and middleware for querying the MusicBrainz.

import createDebug from 'debug';
import DataLoader from 'dataloader';
import LRUCache from 'lru-cache';
import { ONE_DAY, toPlural } from './util.js';

const debug = createDebug('graphbrainz:loaders');

export default function createLoaders(client) {
  // All loaders share a single LRU cache that will remember 8192 responses,
  // each cached for 1 day.
  const cache = new LRUCache({
    max: parseInt(process.env.GRAPHBRAINZ_CACHE_SIZE || 8192, 10),
    maxAge: parseInt(process.env.GRAPHBRAINZ_CACHE_TTL || ONE_DAY, 10),
    dispose(key) {
      debug(`Removed from cache. key=${key}`);
    },
  });
  // Make the cache Map-like.
  cache.delete = cache.del;
  cache.clear = cache.reset;

  const lookup = new DataLoader(
    (keys) => {
      return Promise.all(
        keys.map((key) => {
          const [entityType, id, params = {}] = key;
          return client.lookup(entityType, id, params).then((entity) => {
            if (entity) {
              // Store the entity type so we can determine what type of object this
              // is elsewhere in the code.
              entity._type = entityType;
            }
            return entity;
          });
        })
      );
    },
    {
      batch: false,
      cacheKeyFn: (key) => client.getLookupURL(...key),
      cacheMap: cache,
    }
  );

  const browse = new DataLoader(
    (keys) => {
      return Promise.all(
        keys.map((key) => {
          const [entityType, params = {}] = key;
          return client.browse(entityType, params).then((list) => {
            list[toPlural(entityType)].forEach((entity) => {
              // Store the entity type so we can determine what type of object this
              // is elsewhere in the code.
              entity._type = entityType;
            });
            return list;
          });
        })
      );
    },
    {
      batch: false,
      cacheKeyFn: (key) => client.getBrowseURL(...key),
      cacheMap: cache,
    }
  );

  const search = new DataLoader(
    (keys) => {
      return Promise.all(
        keys.map((key) => {
          const [entityType, query, params = {}] = key;
          return client.search(entityType, query, params).then((list) => {
            list[toPlural(entityType)].forEach((entity) => {
              // Store the entity type so we can determine what type of object this
              // is elsewhere in the code.
              entity._type = entityType;
            });
            return list;
          });
        })
      );
    },
    {
      batch: false,
      cacheKeyFn: (key) => client.getSearchURL(...key),
      cacheMap: cache,
    }
  );

  return { lookup, browse, search };
}