Review List Service

In this lesson, we'll implement the functionality to list restaurant reviews with sorting and pagination capabilities.

Service Implementation

Let's declare the listReviews method in our ReviewService interface:

public interface ReviewService {
    // ...
    Page<Review> listReviews(String restaurantId, Pageable pageable);
}

The method accepts three parameters:

restaurantId - identifies the restaurant whose reviews we want to retrieve
pageable - contains pagination information like page size, number and sorting preferences

The implementation in ReviewServiceImpl handles sorting and pagination manually because reviews are stored as nested objects within the restaurant document:

@Override
public Page<Review> getRestaurantReviews(String restaurantId, Pageable pageable) {
    // Get the restaurant or throw an exception if not found
    Restaurant restaurant = getRestaurantOrThrow(restaurantId);

    // Create a list of reviews
    List<Review> reviews = new ArrayList<>(restaurant.getReviews());

    // Apply sorting based on the Pageable's Sort
    Sort sort = pageable.getSort();

    if (sort.isSorted()) {
        Sort.Order order = sort.iterator().next();
        String property = order.getProperty();
        boolean isAscending = order.getDirection().isAscending();

        Comparator<Review> comparator = switch (property) {
            case "datePosted" -> Comparator.comparing(Review::getDatePosted);
            case "rating" -> Comparator.comparing(Review::getRating);
            default -> Comparator.comparing(Review::getDatePosted);
        };

        reviews.sort(isAscending ? comparator : comparator.reversed());
    } else {
        // Default sort by date descending
        reviews.sort(Comparator.comparing(Review::getDatePosted).reversed());
    }

    // Calculate pagination boundaries
    int start = (int) pageable.getOffset();

    // Handle empty pages
    if (start >= reviews.size()) {
        return new PageImpl<>(Collections.emptyList(), pageable, reviews.size());
    }

    int end = Math.min((start + pageable.getPageSize()), reviews.size());

    // Create the page of reviews
    return new PageImpl<>(reviews.subList(start, end), pageable, reviews.size());
}

Manual Pagination Considerations

We implement manual pagination because reviews are stored as nested objects within the restaurant document.

Using a separate index for reviews would eliminate the need for manual pagination, but would require:

Additional data synchronization logic
More complex data consistency checks
Increased storage requirements

For our use case, the benefits of keeping reviews nested within restaurants outweigh the cost of manual pagination implementation.

Summary

Implemented listReviews method in ReviewService
Added sorting options for reviews by date and rating
Implemented manual pagination for nested review objects
Reviews are retrieved from the restaurant document