JPA with Spring

To use JPA with Spring we need to implement the next 4 steps.

Define mapping metadata in entities

Use the next annotations:

• Entity: Mandatory. Marks the class as a JPA persistent class
• Table: Specifies the exact table name to use on the DB (would be the class name if unspecified)
• Id: Mandatory. Indicates the field to use as the primary key on the database
• Column: Name of the column on the table (would be the field name if unspecified)
• OneToMany: Identifies the field on the 'one' side of a one to many relationship
• JoinColumn: Identifies the column on the 'many' table containing the column to be used when joining. Usually a foreign key.
• Transient: Not stored in database

@Entity
@Table(name="T_ACCOUNT")
public class Account {

    @Id
    @Column(name="ID")
    private Long entityId;

    @Transient
    private String number;
    ...
}

Define an EntityManagerFactory bean

    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory() {
        HibernateJpaVendorAdapter adapter = new HibernateJpaVendorAdapter();
        adapter.setShowSql(true);
        adapter.setGenerateDdl(true); // creating/updating tables (be careful)
        adapter.setDatabase(Database.HSQL);
        Properties props = new Properties();
        props.setProperty("hibernate.format_sql", "true");
        LocalContainerEntityManagerFactoryBean emfb = 
            new LocalContainerEntityManagerFactoryBean();
        emfb.setDataSource(dataSource());
        emfb.setPackagesToScan("com");
        emfb.setJpaProperties(props);
        emfb.setJpaVendorAdapter(adapter);
        return emfb;
    }

Define Transaction Manager and DataSource beans

    @Bean
    public PlatformTransactionManager transactionManager(EntityManagerFactory emf) {
        return new JpaTransactionManager(emf);
    }

    @Bean
    public DataSource dataSource(){
        return
            (new EmbeddedDatabaseBuilder())
            .addScript("classpath:schema.sql")
            .addScript("classpath:data.sql")
            .build();
    }

Define Repository/DAO

@Repository("accountRepository")
public class JpaAccountRepository implements AccountRepository {

    @PersistenceContext
    private EntityManager entityManager;

    @Override
    public Account findByNumber(String number) {
        String jpql = "SELECT a FROM Account a where a.number = :number";
        Account account = entityManager.createQuery(jpql, Account.class)
                .setParameter("number", number).getSingleResult();
        return account;
    }
}