Spring + JPA + H2 Strange behaviours of lazy fetch and bidirectional OneToMany - spring

Question

I have been playing for a long time with JPA, in the past through EJBs, now with Spring. I have recently noticed some weird behaviours I can hardly explain.
First the bidirectionnal OneToMany
My bidirectional OneToMany is correctly set with a mappedBy.
#Entity
public class EntityOne {
#Id #GeneratedValue
private int id;
#OneToMany(mappedBy = "one")
private Set<EntityTwo> twos;
...
#Entity
public class EntityTwo {
#Id #GeneratedValue
private int id;
#ManyToOne
private EntityOne one;
...
Then this does not update the database :
#Transactional
public void firstWay(){
EntityOne e1=em.find(EntityOne.class,1);
EntityTwo e2=em.find(EntityTwo.class,1);
e1.getTwos().add(e2);
}
while this does :
#Transactional
public void secondWay(){
EntityOne e1=em.find(EntityOne.class,1);
EntityTwo e2=em.find(EntityTwo.class,1);
e2.setOne(e1);
}
I am quite puzzled...
Then the lazy fetch :
// this is just a tool example...
public void someFindBy() {
EntityOne e1=em.find(EntityOne.class,1);
for (EntityTwo e2:e1.getTwos()) {
System.out.println(e2);
}
}
leads to LazyExceptionError... Shouldn't my "e1" entity remain attached until the end of the method and thus hibernate resolve the fetch (I use the default persistence context ,i.e. Transaction scoped. I did also try to make the method transactional by annotating it with #Transactional but that didn't change anything).
So, well, I could use an Entity Graph or a Join Fetch, but, still, I wonder why it doesn't work as is...
Here is the Spring configuration file :
#Configuration
#ComponentScan(basePackages = {"facade"})
#EnableTransactionManagement
public class ClientWebConfig extends WebMvcConfigurerAdapter {
#Bean
public DataSource dataSource() {
EmbeddedDatabaseBuilder builder = new EmbeddedDatabaseBuilder();
EmbeddedDatabase db = builder
.setType(EmbeddedDatabaseType.H2)
.build();
return db;
}
#Bean
public LocalContainerEntityManagerFactoryBean entityManagerFactory() {
LocalContainerEntityManagerFactoryBean em
= new LocalContainerEntityManagerFactoryBean();
em.setDataSource(dataSource());
em.setPackagesToScan(new String[] { "model" });
JpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
em.setJpaVendorAdapter(vendorAdapter);
em.setJpaProperties(additionalProperties());
return em;
}
Properties additionalProperties() {
Properties properties = new Properties();
properties.setProperty("hibernate.hbm2ddl.auto", "create-drop");
properties.setProperty(
"hibernate.dialect", "org.hibernate.dialect.H2Dialect");
properties.setProperty("hibernate.hbm2ddl.import_files" ,"insert-data.sql");
return properties;
}
#Bean
public PlatformTransactionManager transactionManager(
EntityManagerFactory emf){
JpaTransactionManager transactionManager = new JpaTransactionManager();
transactionManager.setEntityManagerFactory(emf);
return transactionManager;
}
#Bean
public PersistenceExceptionTranslationPostProcessor exceptionTranslation(){
return new PersistenceExceptionTranslationPostProcessor();
}
}

Answer 1

fix this entity.
cascade, fetch must be set to update.
#Entity
public class EntityOne {
#Id #GeneratedValue
private int id;
**#OneToMany(mappedBy = "one", cascade = CascadeType.ALL, fetch = FetchType.LAZY, orphanRemoval = true)**
private Set<EntityTwo> twos;