Planned lessonJNR-013-L04

Repositories: data access behind an interface

On This Lesson 4 topics

This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.

In this lesson

hide storage behind an interface.

The repository interface says what you can store and find, not how.
In this phase the implementation is in memory (a Map); JNR-P4 swaps in a database.
The service depends on the interface, so it does not change when storage does.
@Repository marks the implementation.

Draft outline details

java

interface ProductRepository {
    Optional<Product> findById(long id);
    List<Product> findAll();
}

Why return Optional?

Show answer

A product may not exist; the type says so.

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