fix(api): db error on duplicate music library import

When the spotify crawler loop would import an artist multiple
times in parallel the first would succeed but the following queries
would throw with following exception:

    QueryFailedError: duplicate key value violates unique constraint "IDX_ARTIST_SPOTIFY_ID"

This error also could happen for the album or track.

src/database/error-codes.ts

@@ -0,0 +1,8 @@
+/**
+ * Offical postgres error codes to match against when checking database exceptions.
+ *
+ * https://www.postgresql.org/docs/current/errcodes-appendix.html
+ */
+export enum PostgresErrorCodes {
+  UNIQUE_VIOLATION = "23505",
+}

src/music-library/music-library.service.ts

@@ -1,4 +1,5 @@
 import { Injectable } from "@nestjs/common";
+import { PostgresErrorCodes } from "../database/error-codes";
 import { Album } from "./album.entity";
 import { AlbumRepository } from "./album.repository";
 import { Artist } from "./artist.entity";
@@ -32,7 +33,20 @@ export class MusicLibraryService {
     artist.name = data.name;
     artist.spotify = data.spotify;
 
-    await this.artistRepository.save(artist);
+    try {
+      await this.artistRepository.save(artist);
+    } catch (err) {
+      if (
+        err.code === PostgresErrorCodes.UNIQUE_VIOLATION &&
+        err.constraint === "IDX_ARTIST_SPOTIFY_ID"
+      ) {
+        // Multiple simultaneous importArtist calls for the same artist were
+        // executed and it is now available in the database for use to retrieve
+        return this.findArtist({ spotify: { id: data.spotify.id } });
+      }
+
+      throw err;
+    }
 
     return artist;
   }
@@ -50,7 +64,18 @@ export class MusicLibraryService {
     album.artists = data.artists;
     album.spotify = data.spotify;
 
-    await this.albumRepository.save(album);
+    try {
+      await this.albumRepository.save(album);
+    } catch (err) {
+      if (
+        err.code === PostgresErrorCodes.UNIQUE_VIOLATION &&
+        err.constraint === "IDX_ALBUM_SPOTIFY_ID"
+      ) {
+        // Multiple simultaneous importAlbum calls for the same album were
+        // executed and it is now available in the database for use to retrieve
+        return this.findAlbum({ spotify: { id: data.spotify.id } });
+      }
+    }
 
     return album;
   }
@@ -69,7 +94,18 @@ export class MusicLibraryService {
     track.album = data.album;
     track.spotify = data.spotify;
 
-    await this.trackRepository.save(track);
+    try {
+      await this.trackRepository.save(track);
+    } catch (err) {
+      if (
+        err.code === PostgresErrorCodes.UNIQUE_VIOLATION &&
+        err.constraint === "IDX_TRACK_SPOTIFY_ID"
+      ) {
+        // Multiple simultaneous findTrack calls for the same track were
+        // executed and it is now available in the database for use to retrieve
+        return this.findTrack({ spotify: { id: data.spotify.id } });
+      }
+    }
 
     return track;
   }