如何使用JPA和Hibernate复制INSERT/UPDATE/DELETE语句

Question

我想以一种可以为我的系统恢复的方式重命名PostgreSQL(9.6)表(一个使用JPA/Hibernate的Java应用程序)

在我的java代码中,JPA实体将具有以下注释@Entity @Table(name="old_name"),并且数据库将具有名为的等效表old_name.

我想以new_name一种我可以逐步更新数据库和Java应用程序的方式重命名表,允许失败和回滚.

典型的步骤是

1. 创建的副本old_name中new_name
2. 确保两者都可用的读/写(即数据以双向方式复制)
3. 更新java应用程序以使用新表 new_name
4. 确保系统更新完成后,删除 old_name

实际上,我希望在同一模式中具有相同数据的重复表,它们都能够接受读取和写入,可以从JPA实体读取.

我知道触发器的使用,并希望避免这种情况.我希望有一种我不知道的技术,并且没有发现这会比使用触发器减少痛苦.

我试图重命名表并在其上创建一个"简单视图",但是JPA实体抱怨因为它找不到具有视图名称的表.(因为它是一个视图,而不是一个表:)并且似乎没有@View/@Table JPA注释将处理这个)

我还没有尝试过这里列出的设施:http://wiki.postgresql.org/wiki/Replication,_Clustering,_and_Connection_Pooling,因为大多数似乎是关于池,分片,我需要一个简单的短期表复制品,但是我也会调查这些.

谢谢 - 我当然希望最简单的选择,更喜欢内置于postgres/JPA的内容,但也会认真考虑第三方选项.

Answer 1

数据库表

假设您有以下两个表:

CREATE TABLE old_post (
    id int8 NOT NULL,
    title varchar(255),
    version int4 NOT NULL,
    PRIMARY KEY (id)
)

CREATE TABLE post (
    id int8 NOT NULL,
    created_on date, 
    title varchar(255),
    version int4 NOT NULL,
    PRIMARY KEY (id)
)

JPA实体

old_post必须使用较新的表复制该表post.请注意,该post表现在具有比旧表更多的列.

我们只需要映射Post实体:

@Entity(name = "Post")
@Table(name = "post")
public static class Post {

    @Id
    private Long id;

    private String title;

    @Column(name = "created_on")
    private LocalDate createdOn = LocalDate.now();

    @Version
    private int version;

    //Getters and setters omitted for brevity
}

Hibernate事件监听器

现在,我们必须注册3个事件侦听器来拦截Post实体的INSERT,UPDATE和DELETE操作.

我们可以通过以下事件监听器来完成此操作:

public class ReplicationInsertEventListener 
        implements PostInsertEventListener {

    public static final ReplicationInsertEventListener INSTANCE = 
        new ReplicationInsertEventListener();

    @Override
    public void onPostInsert(
            PostInsertEvent event) 
            throws HibernateException {
        final Object entity = event.getEntity();

        if(entity instanceof Post) {
            Post post = (Post) entity;

            event.getSession().createNativeQuery(
                "INSERT INTO old_post (id, title, version) " +
                "VALUES (:id, :title, :version)")
            .setParameter("id", post.getId())
            .setParameter("title", post.getTitle())
            .setParameter("version", post.getVersion())
            .setFlushMode(FlushMode.MANUAL)
            .executeUpdate();
        }
    }

    @Override
    public boolean requiresPostCommitHanding(
            EntityPersister persister) {
        return false;
    }
}

public class ReplicationUpdateEventListener 
    implements PostUpdateEventListener {

    public static final ReplicationUpdateEventListener INSTANCE = 
        new ReplicationUpdateEventListener();

    @Override
    public void onPostUpdate(
            PostUpdateEvent event) {
        final Object entity = event.getEntity();

        if(entity instanceof Post) {
            Post post = (Post) entity;

            event.getSession().createNativeQuery(
                "UPDATE old_post " +
                "SET title = :title, version = :version " +
                "WHERE id = :id")
            .setParameter("id", post.getId())
            .setParameter("title", post.getTitle())
            .setParameter("version", post.getVersion())
            .setFlushMode(FlushMode.MANUAL)
            .executeUpdate();
        }
    }

    @Override
    public boolean requiresPostCommitHanding(
            EntityPersister persister) {
        return false;
    }
}

public class ReplicationDeleteEventListener 
        implements PreDeleteEventListener {

    public static final ReplicationDeleteEventListener INSTANCE = 
        new ReplicationDeleteEventListener();

    @Override
    public boolean onPreDelete(
            PreDeleteEvent event) {
        final Object entity = event.getEntity();

        if(entity instanceof Post) {
            Post post = (Post) entity;

            event.getSession().createNativeQuery(
                "DELETE FROM old_post " +
                "WHERE id = :id")
            .setParameter("id", post.getId())
            .setFlushMode(FlushMode.MANUAL)
            .executeUpdate();
        }

        return false;
    }
}

可以使用Hibernate注册3个事件侦听器Integrator:

public class ReplicationEventListenerIntegrator 
        implements Integrator {

    public static final ReplicationEventListenerIntegrator INSTANCE = 
        new ReplicationEventListenerIntegrator();

    @Override
    public void integrate(
            Metadata metadata,
            SessionFactoryImplementor sessionFactory,
            SessionFactoryServiceRegistry serviceRegistry) {

        final EventListenerRegistry eventListenerRegistry =
                serviceRegistry.getService(EventListenerRegistry.class);

        eventListenerRegistry.appendListeners(
            EventType.POST_INSERT, 
            ReplicationInsertEventListener.INSTANCE
        );

        eventListenerRegistry.appendListeners(
            EventType.POST_UPDATE, 
            ReplicationUpdateEventListener.INSTANCE
        );

        eventListenerRegistry.appendListeners(
            EventType.PRE_DELETE, 
            ReplicationDeleteEventListener.INSTANCE
        );
    }

    @Override
    public void disintegrate(
            SessionFactoryImplementor sessionFactory,
            SessionFactoryServiceRegistry serviceRegistry) {

    }
}

并且,为了指示Hibernate使用此自定义Integrator,您需要设置hibernate.integrator_provider配置属性:

<property name="hibernate.integrator_provider"
          value="com.vladmihalcea.book.hpjp.hibernate.listener.ReplicationEventListenerIntegrator "/>

测试时间

现在,当持久化Post实体时:

Post post1 = new Post();
post1.setId(1L);
post1.setTitle(
    "The High-Performance Java Persistence book is to be released!"
);

entityManager.persist(post1);

Hibernate将执行以下SQL INSERT语句:

Query:["INSERT INTO old_post (id, title, version) VALUES (?, ?, ?)"], Params:[(1, The High-Performance Java Persistence book is to be released!, 0)]

Query:["insert into post (created_on, title, version, id) values (?, ?, ?, ?)"], Params:[(2018-12-12, The High-Performance Java Persistence book is to be released!, 0, 1)]

在执行另一个更新现有Post实体并创建新Post实体的事务时:

Post post1 = entityManager.find(Post.class, 1L);
post1.setTitle(post1.getTitle().replace("to be ", ""));

Post post2 = new Post();
post2.setId(2L);
post2.setTitle(
    "The High-Performance Java Persistence book is awesome!"
);

entityManager.persist(post2);

Hibernate old_post也会将所有操作复制到表中:

 Query:["select tablerepli0_.id as id1_1_0_, tablerepli0_.created_on as created_2_1_0_, tablerepli0_.title as title3_1_0_, tablerepli0_.version as version4_1_0_ from post tablerepli0_ where tablerepli0_.id=?"], Params:[(1)]

 Query:["INSERT INTO old_post (id, title, version) VALUES (?, ?, ?)"], Params:[(2, The High-Performance Java Persistence book is awesome!, 0)]

 Query:["insert into post (created_on, title, version, id) values (?, ?, ?, ?)"], Params:[(2018-12-12, The High-Performance Java Persistence book is awesome!, 0, 2)]

 Query:["update post set created_on=?, title=?, version=? where id=? and version=?"], Params:[(2018-12-12, The High-Performance Java Persistence book is released!, 1, 1, 0)]

 Query:["UPDATE old_post SET title = ?, version = ? WHERE id = ?"], Params:[(The High-Performance Java Persistence book is released!, 1, 1)]

删除Post实体时:

Post post1 = entityManager.getReference(Post.class, 1L);
entityManager.remove(post1);

该old_post记录也被删除:

Query:["DELETE FROM old_post WHERE id = ?"], Params:[(1)]
Query:["delete from post where id=? and version=?"], Params:[(1, 1)]

有关更多详细信息,请查看此文章.

代码可在GitHub上获得.