add song to show

src/app/modules/shows/services/show-song.service.ts

@@ -0,0 +1,16 @@
+import {Injectable} from '@angular/core';
+import {ShowSongDataService} from './show-song-data.service';
+
+@Injectable({
+  providedIn: 'root'
+})
+export class ShowSongService {
+
+  constructor(private showSongDataService: ShowSongDataService) {
+  }
+
+  public async new$(showId: string, songId: string): Promise<string> {
+    const data = {songId};
+    return await this.showSongDataService.add(showId, data);
+  }
+}