spring-data-jpa hibernate : failed to lazily initialize a collection, could not initialize proxy - no Session - spring-boot

Question

I am getting this error(intermittently) when I tried to lazily read a list of child entities.
failed to lazily initialize a collection of role: G.h, could not initialize proxy - no Session
I have gone through a list of posts on SO, regarding this error. All I could find is to do EAGER fetch or to use hibernate.enable_lazy_load_no_trans property. I do not want to do either as they are anti patterns.
And I do have #Tranastional(readOnly=true) on the class level where I am reading the data from database, so I would expect the hibernate session to be open till the transaction is complete.
Further more, this error pops up only once in a while. Most of the times there are no issues at all. One more thing is that, I can confirm the entities are loaded lazily(except for place where i have EAGER specified explicitly) as I can see the sql statements being logged, as and when the entities are read.
Here is how my code looks like in a nut shell.
#Service
#Transactional(readOnly = true)
public class AService {
public void someMethod(Long id) {
Optional<A> a = ARepository.findById(id); // This is a standard JPA repository interface where I have defined a method findById
final Optional<G> g = getG(a.get());
if (g.isPresent()) {
for (final H h : g.get().getH()) { // Exception is thrown exactly at line ..getH()
}
}
}
private Optional<G> getG(final A a) {
return a.getB()
.getD()
.getF()
.flatMap(F::getG);
}
}
#Entity
public class A implements Serializable {
#ManyToOne
private AGroup aGroup;
#Transient
public Optional<B> getB() {
return getC().map(C::getB);
}
public Optional<C> getC() {
if (aGroup != null) {
return Optional.ofNullable(aGroup.getC());
}
return empty();
}
}
#Entity
public class AGroup implements Serializable {
#ManyToOne
private C c;
#OneToMany(fetch = EAGER, cascade = ALL, mappedBy = "aGroup")
private final Set<A> as = new HashSet<>();
}
#Entity
public class C implements Serializable {
#OneToMany(fetch = LAZY, cascade = ALL, mappedBy = "c")
private List<AGroup> aGroups = new ArrayList<>();
#ManyToOne
private B b;
}
#Entity
public class B implements Serializable {
#OneToMany(fetch = LAZY, mappedBy = "b")
private Set<C> cs = new HashSet<>();
#ManyToOne(fetch = LAZY)
private D d;
}
#Entity
public class D implements Serializable {
#OneToMany(fetch = LAZY, mappedBy = "d")
private final List<B> bs = new ArrayList<>();
public Optional<F> getF() {
// based on some other fields return Optional.of(F)
}
}
#Entity
public class F implements Serializable {
#ManyToOne
private G g;
public Optional<G> getG() {
return Optional.ofNullable(g);
}
}
#Entity
public class G implements Serializable {
#OneToMany(mappedBy = "g")
private List<F> fs = new ArrayList<>();
#OneToMany(cascade = ALL, mappedBy = "g")
private List<H> hs = new ArrayList<>();
}
#Entity
public class H {
#ManyToOne
private G g;
}
Anyone has any idea what is causing this issue (even more important is, why does this happen intermittently)
I am using spring-data-jpa. This is a spring-boot project. The request comes from the web layer(Rest Controller)

Answer 1

It looks like the underlying Hibernate session is closed/reopened at some point which makes G detached. I don't know what ARepository.findById does or what kind of interceptors you have.