My database is composed of two tables: Organisation and User, in a ManyToOne relationship, where an organisation can hold many users.

Before I share my problem, here are my entities:

@Entity
@Table(name = "organisation")
public class OrganisationEntity {
    @Id
    @Column(name = "orga_id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @NotNull
    private String name;

    // Getters & Setters
}

-

@Entity
@Table(name = "\"user\"")
public class UserEntity {

    @Id
    @Column(name = "user_id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @NotNull
    private String email;

    @NotNull
    private String firstName;

    @NotNull
    private String lastName;

    @NotNull
    private String password;

    @ManyToOne(targetEntity = OrganisationEntity.class,cascade = CascadeType.ALL)
    @JoinColumn(name = "orga_id")
    private OrganisationEntity organisation;

    // Getters & Setters    
}

Here is my issue, when two users are assigned an organisation with the same name, said organisation is created twice in the Organisation table with 2 different ID's. I wish to assign an organisation's ID to a new user if it already exists.

So if users U1 & U2 are created with an organisation called O1, both should have the same orga_id and only one organisation entry should be created in the database.

How can that be achieved? And what is missing in my understanding of Hibernate?

On request, here is my service that creates the UserEntity upon user registration:

@Override
public UserInfo createUser(UserInfo newUser) {
    return mapper.map(userDao.save(mapper.map(newUser)));
}

I map the object with Mapstruct to a UserEntity and send it to my DAO in order to save it in my database.