Spring数据：管理双向多对多关系

Question

我在角色和作用域之间具有双向多对多关系。在CascadeType.Persist的帮助下创建两个实体，甚至创建它们的子实体都是简单明了的。

@Entity
@Table(uniqueConstraints = @UniqueConstraint(name = "role_name", columnNames = "name"))
public class Role {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    private String name;
    
    @ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.PERSIST, mappedBy = "roles")
    private Set<Scope> scopes;

}

@Entity
@Table(uniqueConstraints = @UniqueConstraint(name = "scope_name", columnNames = "name"))
public class Scope {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    private String name;

    @JoinTable(name = "role_scopes", joinColumns = @JoinColumn(name = "scope_id"), inverseJoinColumns = @JoinColumn(name = "role_id"))
    @ManyToMany(cascade = CascadeType.REMOVE)
    private Set<Role> roles;

}

public interface RoleRepository extends CrudRepository<Role, Long> {}
public interface ScopeRepository extends CrudRepository<Scope, Long> {}

Role adminRole = roleRepository.save(new Role("ADMIN"));
Scope allReadScope = scopeRepository.save(new Scope("all.read"));
Scope allWriteScope = scopeRepository.save(new Scope("all.write"));

角色和作用域都可以在CascadeType.Persist的帮助下轻松地自动持久化，如下所示：

Role managedRole = roleRepository.save(new Role("ADMIN", new Scope("all.read"), new Scope("all.write")));

然而...更新ManagedRole会导致org.hibernate.PersistentObjectException：已分离的实体传递给Persist异常：

managedRole.getScopes().remove(allReadScope);
roleRepository.save(managedRole); // PersistentObjectException!

我尝试修改角色::Scopes的CascadeType以包括分离、合并和/或刷新，但未成功。我们怎么绕过这件事？

Answer 1

最有可能的是您面临问题，因为您没有在双向映射中维护关系的双方。让我们在role中这样说：

void add(Scope scope) {
   this.scopes.add(scope);
   scope.getRoles().add(this);
}

老实跟你说，我会完全退出双向映射。维持这是一个真正的噩梦。