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我有两个类 Policy 和 Acl。他们有一个多对多的关系。

// 政策

public class PolicyEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    @Column(name = "POLICY_ID")
    private int policyId;   
    @Column(name = "POLICY_NAME")
    private String policyName;
    @ManyToMany(cascade = CascadeType.PERSIST)
    @JoinTable(name = "POLICY_ACL",joinColumns=@JoinColumn(name = "POLICY_ID"),
                                    inverseJoinColumns=@JoinColumn(name = "ACL_ID"))
    private List<AclEntity> aclList = new ArrayList<AclEntity>();
}

// Acl

public class AclEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    @Column(name = "ACL_ID")
    private int aclId;  
    @Column(name = "ACL_NAME")
    private String aclName;
    @ManyToMany(mappedBy = "aclList")
    private List<PolicyEntity> policyList = new ArrayList<PolicyEntity>();
}

现在，当我使用 Cascade 类型作为 persist 时，我收到以下错误：

Hibernate: insert into POLICY (POLICY_NAME, POLICY_ID) values (?, ?)
Hibernate: insert into POLICY_ACL (POLICY_ID, ACL_ID) values (?, ?)
Exception in thread "main" org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: hibernate.AclEntity

而当我全部使用级联类型时，它会成功保存策略实体和 acl 实体。我无法理解这是如何发生的。注意：我只是在执行保存操作。

这是主要代码：

public static void main(String[] args) {

        PolicyEntity policyEntity = new PolicyEntity();
        AclEntity aclEntity = new AclEntity();

        //policyEntity.setPolicyId(1);
        policyEntity.setPolicyName("Policy 3");
        //aclEntity.setAclId(1);
        aclEntity.setAclName("Acl 3");

        policyEntity.getAclList().add(aclEntity);

        Configuration configuration = new Configuration().configure();
        StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder().
        applySettings(configuration.getProperties());
        SessionFactory sessionFactory = configuration.buildSessionFactory(builder.build());
        Session session = sessionFactory.openSession();
        session.beginTransaction();

        session.save(policyEntity);

        session.getTransaction().commit();
        session.close();
    }
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1 回答 1

3

使用session.persist()代替session.save()

有关详细信息，请参阅休眠文档：

1)会话.persist()：

使瞬态实例持久化。如果关联映射为 cascade="persist" ，则此操作级联到关联实例

2）会话.save（）：

持久化给定的瞬态实例，首先分配一个生成的标识符。（或者如果使用分配的生成器，则使用标识符属性的当前值。）如果关联映射为cascade="save-update" ，则此操作级联到关联实例

于 2015-04-29T12:37:36.717 回答