Pony.fm/app/models/Commands/ToggleFavouriteCommand.php

<?php

	namespace Commands;

	use Entities\Album;
	use Entities\Favourite;
	use Entities\Playlist;
	use Entities\ResourceUser;
	use Entities\Track;
	use Illuminate\Support\Facades\Auth;
	use Illuminate\Support\Facades\DB;

	class ToggleFavouriteCommand extends CommandBase {
		private $_resourceType;
		private $_resourceId;

		function __construct($resourceType, $resourceId) {
			$this->_resourceId = $resourceId;
			$this->_resourceType = $resourceType;
		}

		/**
		 * @return bool
		 */
		public function authorize() {
			$user = Auth::user();
			return$user != null;
		}

		/**
		 * @throws \Exception
		 * @return CommandResponse
		 */
		public function execute() {
			$typeId = $this->_resourceType . '_id';
			$existing = Favourite::where($typeId, '=', $this->_resourceId)->whereUserId(Auth::user()->id)->first();
			$isFavourited = false;

			if ($existing) {
				$existing->delete();
			} else {
				$fav = new Favourite();
				$fav->$typeId = $this->_resourceId;
				$fav->user_id = Auth::user()->id;
				$fav->created_at = time();
				$fav->save();
				$isFavourited = true;
			}

			$resourceUser = ResourceUser::get(Auth::user()->id, $this->_resourceType, $this->_resourceId);
			$resourceUser->is_favourited = $isFavourited;
			$resourceUser->save();

			$resourceTable = $this->_resourceType . 's';

			// We do this to prevent a race condition. Sure I could simply increment the count columns and re-save back to the db
			// but that would require an additional SELECT and the operation would be non-atomic. If two log items are created
			// for the same resource at the same time, the cached values will still be correct with this method.

			DB::table($resourceTable)->whereId($this->_resourceId)->update(['favourite_count' =>
				DB::raw('(
					SELECT
						COUNT(id)
					FROM
						favourites
					WHERE ' .
						$typeId . ' = ' . $this->_resourceId . ')')]);

			return CommandResponse::succeed(['is_favourited' => $isFavourited]);
		}
	}