How to use

keyBy

function

in

lodash

const scoreLoader = () =>
 new DataLoader(async (scoreIds) => {
  const scores = await Score.find({ _id: { $in: scoreIds } }).exec()
  const scoresById = keyBy(scores, '_id')

  return scoreIds.map((scoreId) => scoresById[scoreId])
 })

function groupByParents(array, options) {
 var arrayByID = keyBy(array, options.customID);

 return array.reduce(function(prev, item) {
  var parentID = property.get(item, options.parentProperty);
  if (!parentID || !arrayByID.hasOwnProperty(parentID)) {
   parentID = options.rootID;
  }

  if (parentID && prev.hasOwnProperty(parentID)) {
   prev[parentID].push(item);
   return prev;
  }

  prev[parentID] = [item];
  return prev;
 }, {});
}

/**
 * Gets the all the player deltas (gains), for every period.
 */
async function getPlayerDeltas(playerId: number) {
 const initial = await InitialValues.findOne({ where: { playerId } });
 const latest = await snapshotService.findLatest(playerId);

 const periodDeltas = await Promise.all(
  PERIODS.map(async period => {
   const deltas = await getPlayerPeriodDeltas(playerId, period, latest, initial);
   return { period, deltas };
  })
 );

 // Turn an array of deltas, into an object, using the period as a key,
 // then include only the deltas array in the final object, not the period fields
 return mapValues(keyBy(periodDeltas, 'period'), p => p.deltas);
}

const mapChanges = (changes, side, toValue) => {
  if (!changes.length) {
    return [];
  }

  const computeLineNumber = side === 'old' ? computeOldLineNumber : computeNewLineNumber;
  const changesByLineNumber = keyBy(changes, computeLineNumber);
  const maxLineNumber = computeLineNumber(last(changes));
  return Array.from({length: maxLineNumber}).map((value, i) => toValue(changesByLineNumber[i + 1]));
}

/**
 * Finds all player snapshots, grouped by period.
 *
 * Ex:
 * {
 *    day: [...],
 *    week: [...],
 *    etc
 * }
 */
async function getAllGrouped(playerId) {
 if (!playerId) {
  throw new BadRequestError(`Invalid player id.`);
 }

 const partials = await Promise.all(
  PERIODS.map(async period => {
   const list = await getAllInPeriod(playerId, period);
   return { period, snapshots: list };
  })
 );

 // Turn an array of snapshots, into an object, using the period as a key,
 // then include only the snapshots array in the final object, not the period fields
 return mapValues(keyBy(partials, 'period'), p => p.snapshots);
}

/**
 * Given a list of groups, it will fetch the member count of each,
 * and inserts a "memberCount" field in every group object.
 */
async function attachMembersCount(groups) {
 /**
  * Will return a members count for every group, with the format:
  * [ {groupId: 35, count: "4"}, {groupId: 41, count: "31"} ]
  */
 const membersCount = await Membership.findAll({
  where: { groupId: groups.map(g => g.id) },
  attributes: ['groupId', [Sequelize.fn('COUNT', Sequelize.col('groupId')), 'count']],
  group: ['groupId']
 });

 /**
  * Convert the counts fetched above, into a key:value format:
  * { 35: 4, 41: 31 }
  */
 const countMap = mapValues(
  keyBy(
   membersCount.map((c: any) => ({ groupId: c.groupId, count: parseInt(c.toJSON().count, 10) })),
   c => c.groupId
  ),
  (c: any) => c.count
 );

 return groups.map(g => ({ ...g, memberCount: countMap[g.id] || 0 }));
}

const memberMap = keyBy(members, 'id');
const memberIds = members.map(m => m.id);

keyBy(
 participantCount.map((c: any) => ({
  competitionId: c.competitionId,

const finalsLeaderboardLoader = () =>
 new DataLoader(async (leaderboardIds) => {
  const leaderboards = await FinalsLeaderboard.find({
   _id: { $in: leaderboardIds }
  }).exec()
  const leaderboardsById = keyBy(leaderboards, '_id')

  return leaderboardIds.map(
   (leaderboardId) => leaderboardsById[leaderboardId]
  )
 })

const qualifiersLeaderboardLoader = () =>
 new DataLoader(async (leaderboardIds) => {
  const leaderboards = await QualifiersLeaderboard.find({
   _id: { $in: leaderboardIds }
  }).exec()
  const leaderboardsById = keyBy(leaderboards, '_id')

  return leaderboardIds.map(
   (leaderboardId) => leaderboardsById[leaderboardId]
  )
 })

const adminLoader = () =>
 new DataLoader(async (adminIds) => {
  const admins = await Admin.find({
   _id: { $in: adminIds }
  }).exec()
  const adminsById = keyBy(admins, '_id')

  return adminIds.map((adminId) => adminsById[adminId])
 })

const competitionLoader = () =>
 new DataLoader(async (competitionIds) => {
  const competitions = await Competition.find({
   _id: { $in: competitionIds }
  }).exec()
  const competitionsById = keyBy(competitions, '_id')

  return competitionIds.map(
   (competitionId) => competitionsById[competitionId]
  )
 })

const venueLoader = () =>
 new DataLoader(async (venueIds) => {
  const venues = await Venue.find({ _id: { $in: venueIds } }).exec()
  const venuesById = keyBy(venues, '_id')

  return venueIds.map((venueId) => venuesById[venueId])
 })

const workoutLoader = () =>
 new DataLoader(async (workoutIds) => {
  const workouts = await Workout.find({ _id: { $in: workoutIds } }).exec()
  const workoutsById = keyBy(workouts, '_id')

  return workoutIds.map((workoutId) => workoutsById[workoutId])
 })

const athleteLoader = () =>
 new DataLoader(async (athleteIds) => {
  const athletes = await Athlete.find({
   _id: { $in: athleteIds }
  }).exec()
  const athletesById = keyBy(athletes, '_id')

  return athleteIds.map((athleteId) => athletesById[athleteId])
 })