How can I lazy create the EntityManagerFactory using Spring Data ORM/JPA?

Question

I'm creating a standalone Java application that uses Spring Data with JPA.

Part of the class that creates the factory for the EntityManagerFactory is below:

@Configuration
@Lazy
public class JpaConfig {

@Bean
public LocalContainerEntityManagerFactoryBean entityManagerFactory(MultiTenantConnectionProvider connProvider,  CurrentTenantIdentifierResolver tenantResolver) {
...
}

The problem is: I can only detect the Hibernate Dialect after the ApplicationContext is initialized, because this information is read from an external configuration service.

Since @Lazy did not work, is there any strategy to avoid creating this bean before it is used, i.e, only create it when another bean injects an instance of EntityManager?

Answer 1

I stumbled upon this issue recently and found a solution that worked. Unfortunately "container" managed beans will be initialized during startup and @Lazy is ignored even if the EntityManager is not injected anywhere.

I fixed it by using an in-memory H2 DB to construct the factory bean during startup and changed it later. I think here's what you can do for your issue.

pom.xml:

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <version>1.4.199</version>
</dependency>

Source code:

@Configuration
public class DataSourceConfig {

    @Bean
    public HikariDataSource realDataSource() {
        ...
    }

    @Bean
    public DataSource localH2DataSource() {
        return new EmbeddedDatabaseBuilder().setType(EmbeddedDatabaseType.H2).build();
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean myEntityManagerFactory() throws PropertyVetoException {
        LocalContainerEntityManagerFactoryBean factoryBean = new LocalContainerEntityManagerFactoryBean();
        
        factoryBean.setDataSource(localH2DataSource());

        HibernateJpaVendorAdapter jpaVendorAdapter = new HibernateJpaVendorAdapter();
        jpaVendorAdapter.setShowSql(true);
        factoryBean.setJpaVendorAdapter(jpaVendorAdapter);

        return factoryBean;
    }
}

@Component
@Lazy
public class Main {

    @Autowired
    private LocalContainerEntityManagerFactoryBean emf;

    @Autowired
    private HikariDataSource realDataSource;

    @PostConstruct
    private void updateHibernateDialect() {
        // read the external config here
        emf.setDataSource(realDataSource);
        
        Properties jpaProperties = new Properties();
        jpaProperties.setProperty("hibernate.dialect", "org.hibernate.dialect.DB2Dialect");
        factoryBean.setJpaProperties(jpaProperties);
    }
}