How can I fix a `LazyInitializationException`? - spring

Question

My User & Transfer entities:
#Entity
#Table(name = "user")
public class User {
// [...]
#OneToMany(mappedBy = "user")
private Collection<Transfer> transfers;
}
#Entity
#Table(name = "transfer")
public class Transfer {
#ManyToOne(cascade = CascadeType.MERGE)
#JoinColumn(name="user_id", updatable=false)
private User user;
}
Where I get the LazyInitializationException:
public void transferToFriend(Requirement requirement) {
Optional<User> optionalUser = userRepository.findById(requirement.getUserId());
if (optionalUser.isPresent() && !Objects.isNull(recipient)) { // LazyInitializationException
// [...] }
}
Console LazyInitializationException:
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.sample.model.User.transfers, could not initialize proxy - no Session
What I've tried:
fetch="EAGER"
spring.jpa.properties.hibernate.enable_lazy_load_no_trans=false
EDIT
I discovered that two #Override methods caused the issue in User:
#Override
public String toString() {
return "User{" +
"id=" + id +
", email='" + email + '\'' +
", password='" + password + '\'' +
", firstName='" + firstName + '\'' +
", lastName='" + lastName + '\'' +
", ibanCode=" + ibanCode +
", bicCode=" + bicCode +
", balance=" + balance +
", friendsList='" + friendsList + '\'' +
", transfers=" + transfers +
'}';
}
#Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
User user = (User) o;
return ibanCode == user.ibanCode && bicCode == user.bicCode && Double.compare(user.balance, balance) == 0 && Objects.equals(id, user.id) && Objects.equals(email, user.email) && Objects.equals(password, user.password) && Objects.equals(firstName, user.firstName) && Objects.equals(lastName, user.lastName) && Objects.equals(friendsList, user.friendsList) && Objects.equals(transfers, user.transfers);
}
Those are needed in my Spring Boot unit tests. How should I fix it?

Answer 1

The default for the #OneToMany annotation is FetchType.LAZY so your collections are loaded lazily.
In order to be able to access the collection after you've retrieved the object you need to be in a transactional context (you need an open session)
When you call:
Optional<User> optionalUser = userRepository.findById(requirement.getUserId());
internally a new session is created, the object is retrieved and as soon as the findById method returns the session is closed.
What you should do is make sure you have an open session whenever you access the lazy collection in your User object (which both the equals method and toString do).
The simplest way is to annotate the transferToFriend method with #Transactional and make sure you call the method from outside your service otherwise (because of the way AOP proxies are handled) no transaction will be created (hence no session).