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

Question

我想以我的系统可恢复的方式重命名 PostgreSQL (9.6) 表（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")并且数据库将具有一个等效的表，称为old_name 。

我想以一种可以增量更新数据库和 Java 应用程序的方式将表重命名为new_name ，允许失败和回滚。

典型的步骤是

1. 在新名称中创建old_name名称的new_name
2. 确保读/写可用（即数据以两种方式复制）
3. 更新 Java 应用程序以使用新表new_name
4. 当自信的系统更新完成后，删除old_name

实际上，我想要一个具有相同数据的相同架构中的重复表，它们都能够接受读取和写入，并且可以从 JPA 实体中读取。

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也没有发现的技术可以使这比使用触发器更不痛苦。

我试图重命名该表并在其上创建一个“简单视图”，但是 JPA 实体抱怨说它找不到具有该视图名称的表。 （因为它是一个视图，而不是一个表:)而且似乎没有 @View/@Table JPA 注释可以处理这个问题）

我还没有尝试过这里列出的设施： http ://wiki.postgresql.org/wiki/Replication,_Clustering,_and_Connection_Pooling 因为大多数似乎与池化、分片有关，我需要一个简单的短期表副本，但是我也会调查这些。

谢谢 - 我当然想要最简单的选择，更喜欢 postgres/JPA 内置的东西，但也会认真考虑第 3 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表必须与较新post一起复制。 请注意， post表现在比旧表有更多的列。

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
}

休眠事件监听器

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做到这一点：

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 Integrator注册 3 个事件监听器：

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，要指示 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，当持久化一个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 也将所有操作复制到old_post表：

 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);

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)]

GitHub 上提供的代码。