Cache featured books

Data Layer

03:18

Summary

This lesson demonstrates how to implement a local caching mechanism in the Data Layer using the Hive database in a Clean Architecture Flutter project. After fetching "featured books" from a remote API, the data is saved locally to ensure the app can access content offline or improve load times. The instructor refactors the saving logic into a dedicated helper function to maintain the Single Responsibility Principle, ensuring that data fetching methods do not become overly bloated. This approach keeps the repository's data sources clean, maintainable, and aligned with architectural best practices.

Key Ideas

Hive Box is utilized as the local storage solution to persist book data.
box.addAll(books) provides a simple and efficient way to insert a list of objects into a Hive box.
Single Responsibility Principle dictates that fetching data from a remote source and saving it locally should be distinct operations.
Refactoring code into a reusable helper function (e.g., saveBoxData) improves modularity and reduces redundancy in the HomeRemoteDataSource.

Code Snippets

Final implementation of the reusable saveBoxData helper functiondart

void saveBoxData<T>(List<T> data, String boxName) {
  var box = Hive.box(boxName);
  box.addAll(data);
}

HomeRemoteDataSourceImpl updated to use the helper function for cachingdart

Future<List<BookEntity>> fetchFeaturedBooks() async {
  var data = await apiService.get(
    endpoint: 'volumes?Filtering=free-ebooks&q=programming',
  );
  List<BookEntity> books = getBooksList(data);
  saveBoxData(books, kFeaturedBox);
  return books;
}

Architecture Insight

Architecture insight

Caching is a repo-impl decision, not a use-case or UI one. The use case asks for featured books; the repo decides whether to hit the network, return what's cached, or do both. That's the right home for the policy because it's the only place that sees both sources at once.

Common policies: cache-first with background refresh, network-first with cache fallback, time-based expiry. Each is a few lines in the repo impl — none of them require touching the use case or the widget.

My Notes

The instructor emphasizes maintaining a clean architecture by decoupling the caching logic from the main fetching process. By using a generic function saveBoxData<T>, the code becomes reusable for different types of data boxes, not just books. [Editor's note] While the instructor places this function in lib/utils/functions/, you might consider moving it to a more formal LocalDataSource class in larger projects to adhere strictly to Clean Architecture, which suggests that all data access (local or remote) should be handled within Data Source classes. Remember to always ensure the BookEntity adapter is registered with Hive before any openBox calls to avoid runtime errors.