Repositories

Repositories

Repositories are your gateway to the database. Instead of writing SQL queries yourself, you define an interface and Spring Data JPA does all the heavy lifting. It's like having a personal assistant who handles all your database errands.

You create a repository interface for each entity. For a User entity, you'd create a UserRepository. Spring Data JPA will automatically generate the implementation at runtime. No manual coding needed.

Extending JpaRepository

The magic happens when you extend JpaRepository. This interface gives you a ton of useful methods out of the box. Save, delete, find by ID, find all, count, and more. All for free.

JpaRepository takes two type parameters: the entity type and the ID type. So for a User entity with Long IDs, you'd extend JpaRepository<User, Long>. That's it. You now have a fully functional repository.

public interface UserRepository extends JpaRepository<User, Long> {
}

CRUD Methods

Once you extend JpaRepository, you inherit all the standard CRUD methods. save() creates or updates. findById() gets a single record. findAll() returns everything. deleteById() removes a record.

You can call these methods directly from your service layer. No SQL, no boilerplate, just clean Java code that does exactly what you need.

@Service
public class UserService {
    private final UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public User saveUser(User user) {
        return userRepository.save(user);
    }

    public List<User> getAllUsers() {
        return userRepository.findAll();
    }
}

Custom Query Methods

Spring Data JPA goes beyond basic CRUD. You can define custom query methods just by writing a method name. Spring parses the name and generates the query for you. It's almost magical.

For example, if you need to find a user by email, just add findByEmail(String email) to your repository. Spring Data JPA figures out the rest. No need to write any SQL or JPQL.

public interface UserRepository extends JpaRepository<User, Long> {
    User findByEmail(String email);
    List<User> findByName(String name);
    boolean existsByEmail(String email);
}