Working with Spring Data JPA

Working with Spring Data JPA

Spring Data JPA removes most of the database plumbing from a Boot application. You define an entity, create a tiny repository interface, and Spring Data provides the implementation at runtime, complete with CRUD operations, query methods, and paging.

Define the entity

An entity is a class annotated with @Entity that maps to a table. Fields map to columns, and the primary key is marked with @Id. If you run with an in-memory database like H2, Boot can create the schema for you.

@Entity
public class Customer {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String email;
    protected Customer() {}
}

Create the repository

Extend JpaRepository<Customer, Long> and you immediately get save, findAll, findById, deleteById, and paging support. Spring Data generates the implementation from the interface, so there is no service code to write for basic persistence.

public interface CustomerRepository extends JpaRepository<Customer, Long> {
    List<Customer> findByEmailContaining(String part);
}

Derived query methods

Describe what you want in the method name and Spring Data derives the query: findByEmailContaining, countByStatus, findTop5ByOrderByCreatedAtDesc. Behind the scenes it builds JPQL, and you also have @Query for custom JPQL or native SQL when naming conventions are not enough.

Database configuration

Set the datasource in application.properties with spring.datasource.url, username, and password, plus spring.jpa.hibernate.ddl-auto=update during development so Hibernate aligns tables with entities. Switch to explicit migrations in production.

Transactions

Spring Data repository methods are transactional by default. For multi-step operations, annotate a service method with @Transactional so that a failure rolls back all writes. Keep transactions at the service layer, not inside controllers.

Key Points

• @Entity maps a class to a table; @Id marks the primary key.
• Interface repositories built on JpaRepository provide CRUD instantly.
• Derived method names generate JPQL queries automatically.
• Configure the datasource and DDL strategy in application.properties.
• Put @Transactional on service methods for multi-step writes.