code: function createDataLoader(ds) {
      ds = typeof ds !== 'undefined' ? ds : this && this.ds;
  
      if (!ds) {
          throw new Error('A Datastore instance has to be passed');
      }
  
      return new DataLoader(keys => (
          ds.get(keys).then(([res]) => {
              // When providing an Array with 1 Key item, google-datastore
              // returns a single item.
              // For predictable results in gstore, all responses from Datastore.get()
              // calls return an Array
              const entities = arrify(res);
              const entitiesByKey = {};
              entities.forEach((entity) => {
                  entitiesByKey[keyToString(entity[ds.KEY])] = entity;
              });
  
              return keys.map(key => entitiesByKey[keyToString(key)] || null);
          })
      ), {
          cacheKeyFn: _key => keyToString(_key),
          maxBatchSize: 1000,
      });
  }
docs: Create a DataLoader instance
  @param {Datastore} ds @google-cloud Datastore instance