如何使用Hibernate批处理DELETE语句

介绍

在我以前的文章中，我解释了批处理INSERT和UPDATE语句所需的Hibernate配置。这篇文章将继续本主题的DELETE语句批处理。

领域模型实体

我们将从以下实体模型开始：

注释后细节批处理删除

Post实体与Comment具有一对多关联，并且与PostDetails实体具有一对一关系：

@OneToMany(cascade = CascadeType.ALL, mappedBy = "post",orphanRemoval = true)
private List<Comment> comments = new ArrayList<>();@OneToOne(cascade = CascadeType.ALL, mappedBy = "post",orphanRemoval = true, fetch = FetchType.LAZY)
private PostDetails details;

即将进行的测试将针对以下数据进行：

doInTransaction(session -> {int batchSize = batchSize();for(int i = 0; i < itemsCount(); i++) {int j = 0;Post post = new Post(String.format("Post no. %d", i));        post.addComment(new Comment( String.format("Post comment %d:%d", i, j++)));post.addComment(new Comment(String.format("Post comment %d:%d", i, j++)));post.addDetails(new PostDetails());session.persist(post);if(i % batchSize == 0 && i > 0) {session.flush();session.clear();}}
});

休眠配置

正如已经说明，以下属性所需的配料INSERT和UPDATE语句：

properties.put("hibernate.jdbc.batch_size", String.valueOf(batchSize()));
properties.put("hibernate.order_inserts", "true");
properties.put("hibernate.order_updates", "true");
properties.put("hibernate.jdbc.batch_versioned_data", "true");

接下来，我们将检查DELETE语句是否也被批处理。

JPA级联删除

因为级联实体状态转换很方便，所以我将证明CascadeType.DELETE和JDBC批处理不能很好地混合使用。

以下测试将要进行：

选择一些帖子以及评论和帖子 详细信息
删除帖子，同时将delete事件传播到Comments和PostDetails

@Test
public void testCascadeDelete() {LOGGER.info("Test batch delete with cascade");final AtomicReference<Long> startNanos = new AtomicReference<>();addDeleteBatchingRows();doInTransaction(session -> {List<Post> posts = session.createQuery("select distinct p " +"from Post p " +"join fetch p.details d " +"join fetch p.comments c").list();startNanos.set(System.nanoTime());for (Post post : posts) {session.delete(post);}});LOGGER.info("{}.testCascadeDelete took {} millis",getClass().getSimpleName(),TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startNanos.get()));
}

运行此测试将给出以下输出：

Query:{[delete from Comment where id=? and version=?][55,0]} {[delete from Comment where id=? and version=?][56,0]} 
Query:{[delete from PostDetails where id=?][3]} 
Query:{[delete from Post where id=? and version=?][3,0]} 
Query:{[delete from Comment where id=? and version=?][54,0]} {[delete from Comment where id=? and version=?][53,0]} 
Query:{[delete from PostDetails where id=?][2]} 
Query:{[delete from Post where id=? and version=?][2,0]} 
Query:{[delete from Comment where id=? and version=?][52,0]} {[delete from Comment where id=? and version=?][51,0]} 
Query:{[delete from PostDetails where id=?][1]} 
Query:{[delete from Post where id=? and version=?][1,0]}

仅批注Comment DELETE语句，其他实体在单独的数据库往返中删除。

此行为的原因由ActionQueue排序实现给出：

if ( session.getFactory().getSettings().isOrderUpdatesEnabled() ) {// sort the updates by pkupdates.sort();
}
if ( session.getFactory().getSettings().isOrderInsertsEnabled() ) {insertions.sort();
}

虽然介绍了INSERTS和UPDATES ，但根本不对DELETE语句进行排序。仅当所有语句都属于同一数据库表时，才能重新使用JDBC批处理。当传入语句针对另一个数据库表时，必须释放当前批处理，以便新批处理与当前语句数据库表匹配：

public Batch getBatch(BatchKey key) {if ( currentBatch != null ) {if ( currentBatch.getKey().equals( key ) ) {return currentBatch;}else {currentBatch.execute();currentBatch.release();}}currentBatch = batchBuilder().buildBatch(key, this);return currentBatch;
}

移除孤儿和手动冲洗

一种变通方法是在前进到新的Child关联之前，先手动刷新Hibernate Session，然后解除所有Child实体的关联：

@Test
public void testOrphanRemoval() {LOGGER.info("Test batch delete with orphan removal");final AtomicReference<Long> startNanos = new AtomicReference<>();addDeleteBatchingRows();doInTransaction(session -> {List<Post> posts = session.createQuery("select distinct p " +"from Post p " +"join fetch p.details d " +"join fetch p.comments c").list();startNanos.set(System.nanoTime());posts.forEach(Post::removeDetails);session.flush();posts.forEach(post -> {for (Iterator<Comment> commentIterator = post.getComments().iterator(); commentIterator.hasNext(); ) {Comment comment =  commentIterator.next();comment.post = null;commentIterator.remove();}});session.flush();posts.forEach(session::delete);});LOGGER.info("{}.testOrphanRemoval took {} millis",getClass().getSimpleName(),TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startNanos.get()));
}

这次，所有DELETE语句均已正确批处理：

Query:{[delete from PostDetails where id=?][2]} {[delete from PostDetails where id=?][3]} {[delete from PostDetails where id=?][1]} 
Query:{[delete from Comment where id=? and version=?][53,0]} {[delete from Comment where id=? and version=?][54,0]} {[delete from Comment where id=? and version=?][56,0]} {[delete from Comment where id=? and version=?][55,0]} {[delete from Comment where id=? and version=?][52,0]} {[delete from Comment where id=? and version=?][51,
Query:{[delete from Post where id=? and version=?][2,0]} {[delete from Post where id=? and version=?][3,0]} {[delete from Post where id=? and version=?][1,0]}

SQL级联删除

更好的解决方案是使用SQL级联删除，而不是JPA实体状态传播机制。这样，我们还可以减少DML语句的数量。由于Hibernate Session充当事务后写式缓存，因此在将实体状态转换与数据库端自动操作混合使用时，我们必须格外谨慎，因为持久性上下文可能无法反映最新的数据库更改。

Post实体一对多 注释关联使用Hibernate特定的@OnDelete批注进行标记，以便自动生成的数据库模式包括ON DELETE CASCADE指令：

@OneToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE}, mappedBy = "post")
@OnDelete(action = OnDeleteAction.CASCADE)
private List<Comment> comments = new ArrayList<>();

生成以下DDL ：

alter table Comment add constraint 
FK_apirq8ka64iidc18f3k6x5tc5 foreign key (post_id) 
references Post on delete cascade

使用PostDetails实体一对一的Post关联也可以做到这一点：

@OneToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "id")
@MapsId
@OnDelete(action = OnDeleteAction.CASCADE)
private Post post;

以及相关的DDL ：

alter table PostDetails add constraint 
FK_h14un5v94coafqonc6medfpv8 foreign key (id) 
references Post on delete cascade

CascadeType.ALL和orphanRemoval替换为CascadeType.PERSIST和CascadeType.MERGE ，因为我们不再希望Hibernate传播实体删除事件。

测试仅删除Post实体。

doInTransaction(session -> {List<Post> posts = session.createQuery("select p from Post p").list();startNanos.set(System.nanoTime());for (Post post : posts) {session.delete(post);}
});

由于只有一个目标表，因此DELETE语句已正确批处理。

Query:{[delete from Post where id=? and version=?][1,0]} {[delete from Post where id=? and version=?][2,0]} {[delete from Post where id=? and version=?][3,0]}