private static Option <Domain.Entities.Restaurant, Error> UserShouldNotRateOwnRestaurant(
Domain.Entities.Restaurant restaurant,
Guid userId) =>
restaurant.NoneWhen(r =>
r.OwnerId == userId,
Error.Validation("User cannot rate he/her's own restaurant."));
private static Option <Domain.Entities.Restaurant, Error> RestaurantOwnerShouldRegisterMeal(
Domain.Entities.Restaurant restaurant,
Guid userId) =>
restaurant.NoneWhen(r => r.OwnerId != userId, Error.Unauthorized("Current user is not the restaurant owner!"));