Spring Data JPA

Repositories you don't implement, queries derived from method names, and how Spring Boot wires it all up.

Spring Boot JPA setup

Add spring-boot-starter-data-jpa and a JDBC driver. Boot then auto-configures the DataSource, the EntityManagerFactory (Hibernate by default), a JpaTransactionManager, and enables repositories — you write almost no plumbing.

@Entity
public class Account {
  @Id @GeneratedValue
  private Long id;
  private String email;
  // ...
}

Configure the database in application.properties (spring.datasource.url/username/password). With H2 on the classpath and no URL, Boot even spins up an in-memory database automatically.

The repository hierarchy

Each extends the one above it, so JpaRepository has everything.

public interface AccountRepository extends JpaRepository<Account, Long> {
  // derived queries — no body needed:
  List<Account> findByEmail(String email);
  List<Account> findByActiveTrueOrderByEmailAsc();
}

Derived query methods

Spring parses the method name into a query. The name = a prefix + By + property conditions:

Examples: findByLastName(String), findByAgeGreaterThan(int), findByLastNameAndFirstName(...), countByActiveTrue().

Explicit queries with @Query

When a derived name would be unwieldy, write the query yourself. JPQL by default; native SQL with a flag:

@Query("select a from Account a where a.email = :email")
Account lookup(@Param("email") String email);          // JPQL + named param

@Query(value = "select * from account where email = ?1", nativeQuery = true)
Account lookupNative(String email);                        // native SQL

Check yourself

Derived-query validity and the repository hierarchy are the money questions. Covers your book's whole Spring Data JPA section. Options shuffle on every load.