lazy loading working

Author: Rohanator9000

server/src/entities/Party.ts

@@ -28,21 +28,24 @@ export class Party extends BaseEntity {
   @UpdateDateColumn()
   latestTime: Date
 
-  @ManyToOne(() => Song, { eager: true, nullable: true })
-  currentSong: Song | null
+  @ManyToOne(() => Song, { lazy: true, nullable: true })
+  currentSong: Promise<Song | null>
 
-  @OneToMany(() => VotedSong, votedSong => votedSong.party, { eager: true, cascade: ['remove'] })
-  votedSongs: VotedSong[]
+  @Column({ nullable: true })
+  currentSongId: number
 
-  @OneToMany(() => PlayedSong, playedSong => playedSong.party, { eager: true, cascade: ['remove'] })
-  playedSongs: PlayedSong[]
+  @OneToMany(() => VotedSong, votedSong => votedSong.party, { lazy: true, cascade: ['remove'] })
+  votedSongs: Promise<VotedSong[]>
+
+  @OneToMany(() => PlayedSong, playedSong => playedSong.party, { lazy: true, cascade: ['remove'] })
+  playedSongs: Promise<PlayedSong[]>
 
   constructor(name: string, password?: string) {
     super()
 
     this.name = name
     this.password = password || null
-    this.currentSong = null
+    this.currentSong = Promise.resolve(null)
     // Don't initialize this.playedSongs or this.votedSongs.
     //   this.playedSongs = []
     //   this.votedSongs = []
@@ -55,7 +58,7 @@ export class Party extends BaseEntity {
   }
 
   public async voteForSong(song: Song) {
-    let votedSong = await VotedSong.findOne({ song: song, party: this })
+    let votedSong = await VotedSong.findOne({ where: { songId: song.id, partyId: this.id } })
 
     if (votedSong) {
       await votedSong.incrementVote()
@@ -68,10 +71,14 @@ export class Party extends BaseEntity {
   }
 
   private async removeCurrentSong() {
-    if (this.currentSong) {
-      const newPlayedSong = new PlayedSong(this.currentSong, this, await this.getNextSequenceNumber())
-      this.currentSong = null
-      this.playedSongs.push(newPlayedSong)
+    const currentSong = await this.currentSong
+
+    if (currentSong) {
+      const newPlayedSong = new PlayedSong(currentSong, this, await this.getNextSequenceNumber())
+      this.currentSong = Promise.resolve(null)
+      const playedSongs = await this.playedSongs
+      playedSongs.push(newPlayedSong)
+      this.playedSongs = Promise.resolve(playedSongs)
       await Promise.all([newPlayedSong.save(), this.save()])
     }
   }
@@ -80,50 +87,40 @@ export class Party extends BaseEntity {
     const highestVotedSong = await this.getHighestVotedSong()
 
     if (highestVotedSong) {
-      this.currentSong = highestVotedSong.song
+      this.currentSongId = (await highestVotedSong.getSong()).id
       await Promise.all([highestVotedSong.remove(), this.save()])
     }
   }
 
+  public async getSortedVotedSongs() {
+    const votedSongs = await this.votedSongs
+    const songs = await Promise.all(votedSongs.map(votedSong => votedSong.getSong()))
+    const zipped: [VotedSong, Song][] = votedSongs.map((votedSong, index) => {
+      return [votedSong, songs[index]]
+    })
+    zipped.sort(([votedSong1, song1], [votedSong2, song2]) => {
+      if (votedSong1.count != votedSong2.count) {
+        return votedSong2.count - votedSong1.count
+      }
+      if (song1.title < song2.title) {
+        return -1
+      }
+      return 0
+    })
+    return zipped.map(([votedSong, _song]) => votedSong)
+  }
+
   private async getHighestVotedSong() {
     // TODO: TypeORM can't sort by fields of eagerly joined rows. So we currently retrieve all VotedSong for the party
     //   and then sort by song name and then sort by name among the VotedSong with the highest equivalent count and then
     //   return the first VotedSong. Optimize this by using the TypeORM query builder to build an SQL query that can
     //   JOIN and then order correctly to retrieve a single VotedSong rather than all VotedSong for the party.
-    return VotedSong.find({ where: { party: this }, order: { count: 'DESC' } }).then(votedSongs => {
-      if (!Array.isArray(votedSongs) || !votedSongs.length) {
-        return null
-      } else {
-        const highestCount = votedSongs[0].count
-        return votedSongs
-          .filter(votedSong => votedSong.count == highestCount)
-          .sort((votedSong1, votedSong2) => {
-            if (votedSong1.count != votedSong2.count) {
-              return votedSong2.count - votedSong1.count
-            }
-            if (votedSong1.song.title < votedSong2.song.title) {
-              return -1
-            }
-            return 0
-          })[0]
-      }
-    })
+    const sortedVotedSongs = await this.getSortedVotedSongs()
+    return sortedVotedSongs[0]
   }
 
   private async getNextSequenceNumber() {
     const latestSong = await PlayedSong.findOne({ where: { party: this }, order: { sequenceNumber: 'DESC' } })
     return latestSong ? latestSong.sequenceNumber + 1 : 0
   }
-
-  public sortVotedSongs() {
-    this.votedSongs.sort((votedSong1, votedSong2) => {
-      if (votedSong1.count != votedSong2.count) {
-        return votedSong2.count - votedSong1.count
-      }
-      if (votedSong1.song.title < votedSong2.song.title) {
-        return -1
-      }
-      return 0
-    })
-  }
 }

server/src/entities/PlayedSong.ts

@@ -11,17 +11,33 @@ export class PlayedSong extends BaseEntity {
   @Column()
   sequenceNumber: number
 
-  @ManyToOne(() => Song, { eager: true, nullable: false })
-  song: Song
+  @ManyToOne(() => Song, { lazy: true, nullable: false })
+  song: Promise<Song>
 
-  @ManyToOne(() => Party, party => party.playedSongs, { nullable: false })
-  party: Party
+  @Column()
+  songId: number
+
+  @ManyToOne(() => Party, party => party.playedSongs, { nullable: false, lazy: true })
+  party: Promise<Party>
+
+  @Column()
+  partyId: number
 
   constructor(song: Song, party: Party, sequenceNumber: number) {
     super()
 
-    this.song = song
-    this.party = party
+    this.song = Promise.resolve(song)
+    this.party = Promise.resolve(party)
     this.sequenceNumber = sequenceNumber
   }
+
+  // For some reason the Song or Party fields return Promise<undefined> (I think a TypeORM bug), so we need the following two methods.
+  // Piazza question: https://piazza.com/class/kfpm567u1e24eb?cid=123.
+  public async getParty() {
+    return Party.findOneOrFail(this.partyId)
+  }
+
+  public async getSong() {
+    return Song.findOneOrFail(this.songId)
+  }
 }

server/src/entities/VotedSong.ts

@@ -11,21 +11,37 @@ export class VotedSong extends BaseEntity {
   @Column()
   count: number
 
-  @ManyToOne(() => Song, { eager: true })
-  song: Song
+  @ManyToOne(() => Song, { lazy: true, nullable: false })
+  song: Promise<Song>
 
-  @ManyToOne(() => Party, party => party.votedSongs)
-  party: Party
+  @Column()
+  songId: number
+
+  @ManyToOne(() => Party, party => party.votedSongs, { nullable: false, lazy: true })
+  party: Promise<Party>
+
+  @Column()
+  partyId: number
 
   constructor(song: Song, party: Party) {
     super()
-    this.song = song
-    this.party = party
+    this.song = Promise.resolve(song)
+    this.party = Promise.resolve(party)
     this.count = 1
   }
 
   public async incrementVote() {
     ++this.count
     await this.save()
   }
+
+  // For some reason the Song or Party fields return Promise<undefined> (I think a TypeORM bug), so we need the following two methods.
+  // Piazza question: https://piazza.com/class/kfpm567u1e24eb?cid=123.
+  public async getParty() {
+    return Party.findOneOrFail(this.partyId)
+  }
+
+  public async getSong() {
+    return Song.findOneOrFail(this.songId)
+  }
 }

server/src/graphql/api.ts

@@ -2,6 +2,7 @@ import { readFileSync } from 'fs'
 import { PubSub } from 'graphql-yoga'
 import path from 'path'
 import { Party } from '../entities/Party'
+import { PlayedSong } from '../entities/PlayedSong'
 import { Song } from '../entities/Song'
 import { Resolvers } from './schema.types'
 
@@ -21,7 +22,6 @@ export const graphqlRoot: Resolvers<Context> = {
   Query: {
     party: async (_, { partyName, partyPassword }) => {
       const party = await Party.findOne({ name: partyName, password: partyPassword || null })
-      party?.sortVotedSongs()
       return party || null
     },
     songs: () => Song.find(),
@@ -40,19 +40,39 @@ export const graphqlRoot: Resolvers<Context> = {
     createParty: async (_, { partyName, partyPassword }) => {
       const party = await new Party(partyName, partyPassword || undefined).save()
       await party.reload() // We have to reload() because save() doesn't return the entire Party object.
-      party.sortVotedSongs()
       return party
     },
     nextSong: async (_, { partyId }) => {
       const party = await Party.findOne(partyId)
       await party?.playNextSong()
       await party?.reload()
-      party?.sortVotedSongs()
       return party || null
     },
   },
   // Rely on the resolver chain and async/partial resolution to perform the data conversion necessary for the API.
   Party: {
     latestTime: parent => parent.latestTime.toString(),
+    votedSongs: async self => {
+      return self.getSortedVotedSongs()
+    },
+    playedSongs: async self => {
+      // I cast here because playedSongs.song is a Promise, but I know that we'll just use the PlayedSong resolver to get an actual Song.
+      return (await self.playedSongs) as any
+    },
+    currentSong: async self => {
+      return await self.currentSong
+    },
+  },
+  VotedSong: {
+    song: async self => {
+      return self.getSong()
+    },
+  },
+  PlayedSong: {
+    song: async self => {
+      // For some reason the type of self is not PlayedSong so I have to cast it. TODO: investigate this.
+      const parentPlayedSong = (self as unknown) as PlayedSong
+      return parentPlayedSong.getSong()
+    },
   },
 }