Hibernate：使用带有连接表的双向多对一映射持久化实体 - org.hibernate.PropertyValueException

Question

Hello i am trying to persist one of my entities "Role" which has a many-to-one relation via a join table to my other entity "User". However every time i try to insert role without any users attached i get the following error: org.hibernate.PropertyValueException: not-null property references a null or transient value. My Role entity mapping to User:

@ManyToOne(fetch = FetchType.LAZY, cascade = { CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH,
            CascadeType.DETACH })
    @JoinTable(name = "t_UserRoles", joinColumns = {
            @JoinColumn(name = "cUserRolesRoleId", referencedColumnName = "cRoleId") }, inverseJoinColumns = {
                    @JoinColumn(name = "cUserRolesUserId", referencedColumnName = "cUserId") })
    private User user;

And my User to Role:

@OneToMany(cascade = { CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH, CascadeType.DETACH })
    @JoinTable(name = "t_UserRoles", joinColumns = {
            @JoinColumn(name = "cUserRolesUserId", referencedColumnName = "cUserId") }, inverseJoinColumns = {
                    @JoinColumn(name = "cUserRolesRoleId", referencedColumnName = "cRoleId") })
    private Set<Role> roles;

the code that throws the exception:

...
Role newRole = new Role();
            newRole.setRoleName(roleName);
            roleAfterSave = manager.merge(newRole);
            manager.getTransaction().commit();

The goal is to be able to save the Role without the need to create User instance as well. Things i have already tried:

@ManyToOne(optional = true,...

@JoinColumn(name = "cUserRolesRoleId", referencedColumnName = "cRoleId",nullable = true)

Tell me if you need any more of the code! Thanks for the help in advance!

Answer 1

First of all, is there any reason to have a join table at one-to-many relationship?

I think, either, there should be a "Role definition" table, where role types are defined, but then the Role entity shouldn't be related to concrete user. The relationship should be rather many-to-many. For me, that makes more sense.

Or the Role entity is really related to user, but then I would leave out a join table.