JPA ManyToMany - empty list in findById - spring-boot

Question

In my Spring Boot project I have an entity class User
#NoArgsConstructor
#AllArgsConstructor
#Getter
#Setter
#Builder
#Entity
#Table(name = "applicationusers")
public class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
[...]
#Singular
#ManyToMany(
cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
},
fetch = FetchType.EAGER)
#Fetch(value = FetchMode.SUBSELECT)
#JoinTable(
name = "applicationusers_roles",
joinColumns = { #JoinColumn(name = "applicationuser_id") },
inverseJoinColumns = { #JoinColumn(name = "role_id") }
)
private Set<Role> roles;
}
and a second entity class role
#NoArgsConstructor
#AllArgsConstructor
#Getter
#Setter
#Builder
#Entity
#Table(name = "roles")
public class Role {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(nullable = false, unique = true)
#Length(min = 3, max = 15)
private String name;
#ManyToMany(fetch = FetchType.EAGER, mappedBy = "roles")
#Fetch(value = FetchMode.SUBSELECT)
#Singular
private Set<User> applicationUsers;
}
In one of my tests, I try to store a Role with a User to the repository like this
#Test
public void createRoleWithUsers() {
User newUser = User.builder()
.name("name")
.password("1234567")
.email("hello#world.net")
.enabled(true)
.build();
User savedUser = userRepository.save(newUser);
Set<User> users = new HashSet<>();
users.add(savedUser);
Role role = Role.builder()
.name("TestRole")
.applicationUsers(users)
.build();
Role createdRole = roleRepository.save(role);
Role foundRole = roleRepository.findRoleById(createdRole.getId()).get();
[...]
}
Debugging this code, I found out, that createdRole has the users set as expected but foundRole doesn't.
How can I get the users in foundRole too?
Please tell me if you need the repository-code - it's a very simple interface so I just skipped it.

Answer 1

Simplified response, read the fine manual: 6.3.10. Configuring Fetch- and LoadGraphs.
#NoArgsConstructor
#AllArgsConstructor
#Getter
#Setter
#Builder
#Entity
#Table(name = "applicationusers")
public class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Singular
#ManyToMany
private Set<Role> roles;
}
and
#NoArgsConstructor
#AllArgsConstructor
#Getter
#Setter
#Builder
#Entity
#Table(name = "roles")
public class Role {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#ManyToMany(mappedBy = "roles")
#Singular
private Set<User> applicationUsers;
}
The manual specifies:
public interface RoleRepository extends JpaRepository<Role, Long>{
#Query("select r from Role r where r.id = :id")
#EntityGraph(attributePaths = {"applicationUsers"})
Role findByIdFetchUsers(#Param("id") Long id);
}
The second System.out.println will give you a org.hibernate.LazyInitializationException.
#Override
public void run(String... args) throws Exception {
User u = save();
Role r2 = roleRepository.findByIdFetchUsers(u.getId());
System.out.println("R: " + r2 + " : " + r2.getApplicationUsers());
Role r1 = roleRepository.findById(u.getId()).get();
System.out.println("R: " + r1 + " : " + r1.getApplicationUsers());
}