Spring Data：管理双向多对多关系

Question

Role 和 Scope 之间存在双向多对多关系。在CascadeType.PERSIST 的帮助下创建实体甚至它们的子实体都简单明了。

Role 实体很简单：

@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;

}

还有Scope：

@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;

}

他们的存储库只是 CrudRepository 扩展：

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

下面的 sn-p 举例说明了实体的插入：

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

Role 和Scope 都可以在CascadeType.PERSIST 的帮助下轻松自动持久化，如下所示：

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

但是...更新managedRole 会导致org.hibernate.PersistentObjectException: detached entity passed to persist 异常：

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

我尝试将Role::scopes 的CascadeType 修改为也包括DETACH、MERGE 和/或REFRESH，但没有成功。我们如何解决这个问题？

Answer 1

您很可能会遇到问题，因为您没有在双向映射中维护关系的双方。让我们说Role：

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

老实说，我会完全放弃双向映射。保持这种状态是一场真正的噩梦。