JPA AttributeConverter 使休眠在事务中的整个表上生成更新语句答案

【问题标题】：JPA AttributeConverter makes hibernate generate update statements on whole table in transactionJPA AttributeConverter 使休眠在事务中的整个表上生成更新语句
【发布时间】：2017-08-11 13:13:18
【问题描述】：

这篇文章中的所有代码都可以在这里找到： https://github.com/cuipengfei/gs-accessing-data-jpa/tree/master/complete

您可以运行此测试来重现问题： https://github.com/cuipengfei/gs-accessing-data-jpa/blob/master/complete/src/test/java/hello/T1ServiceTest.java

我有一个领域模型：

@Entity
@Table(name = "t1", schema = "test")
public class T1 extends BaseEntity {

  @Column(nullable = false)
  private UUID someField;

  @Column()
  private ZonedDateTime date;

  public T1(UUID someField, ZonedDateTime date) {
    this.someField = someField;
    this.date = date;
  }
}

它有一个类型为 ZonedDateTime 的字段，所以我有一个转换器将其转换为 sql 时间戳：

@Converter(autoApply = true)
public class ZonedDateTimeAttributeConverter
    implements AttributeConverter<ZonedDateTime, Timestamp> {

  @Override
  public Timestamp convertToDatabaseColumn(ZonedDateTime entityValue) {
    return (entityValue == null) ? null :
        valueOf(entityValue.withZoneSameInstant(of("UTC")).toLocalDateTime());
  }

  @Override
  public ZonedDateTime convertToEntityAttribute(Timestamp databaseValue) {
    return (databaseValue == null) ? null : databaseValue.toLocalDateTime().atZone(
        of("UTC"));
  }
}

当我尝试在这样的事务中创建大量 T1 时：

@Service
public class T1Service {
  private static final Logger log = LoggerFactory.getLogger(T1Service.class);

  @Autowired
  T1Repository t1Repository;

  @Transactional
  public void insertMany() {
    for (int i = 0; i < 1000; i++) {
      log.info("!!! " + (i + 1) + "th item start");

      UUID randomUUID = UUID.randomUUID();
      T1 foundT1 = tryToFindExistingT1(randomUUID);//certainly won't find

      if (foundT1 == null) {
        log.info("t1 not found");
        ZonedDateTime date = now();
        //date = null;
        //if you enable the line above, there won't be any update statements anymore
        //and find will also become faster
        T1 t1 = new T1(randomUUID, date);
        saveT1(t1);
      }

      log.info("!!! " + (i + 1) + "th item finished");
      log.info("====================================");
    }
  }

  private T1 tryToFindExistingT1(UUID someField) {
    long start = currentTimeMillis();
    T1 t1Id = t1Repository.findBySomeField(someField);
    //as nth item increases, the line above will become very very slow
    //and also, there will be more and more update statements
    //but if you set date of t1 to null, update statement will disappear and it'll not be slow
    log.info("find took: " + (currentTimeMillis() - start) + " milliseconds");
    return t1Id;
  }

  private T1 saveT1(T1 t1) {
    long start = currentTimeMillis();
    T1 savedT1 = t1Repository.save(t1);
    log.info("save took: " + (currentTimeMillis() - start) + " milliseconds");
    return savedT1;
  }

}

hibernate会为整个t1表生成更新语句。

这是前几轮 for 循环的日志：

2017-03-20 17:51:54.039  INFO 74789 --- [           main] hello.T1Service                          : !!! 1th item start
2017-03-20 17:51:54.052  INFO 74789 --- [           main] o.h.h.i.QueryTranslatorFactoryInitiator  : HHH000397: Using ASTQueryTranslatorFactory
Hibernate: select t1x0_.id as id1_0_, t1x0_.date as date2_0_, t1x0_.some_field as some_fie3_0_ from test.t1 t1x0_ where t1x0_.some_field=?
2017-03-20 17:51:54.154  INFO 74789 --- [           main] hello.T1Service                          : find took: 114 milliseconds
2017-03-20 17:51:54.154  INFO 74789 --- [           main] hello.T1Service                          : t1 not found
2017-03-20 17:51:54.177  INFO 74789 --- [           main] hello.T1Service                          : save took: 15 milliseconds
2017-03-20 17:51:54.177  INFO 74789 --- [           main] hello.T1Service                          : !!! 1th item finished
2017-03-20 17:51:54.177  INFO 74789 --- [           main] hello.T1Service                          : ====================================
2017-03-20 17:51:54.177  INFO 74789 --- [           main] hello.T1Service                          : !!! 2th item start
Hibernate: insert into test.t1 (date, some_field, id) values (?, ?, ?)
Hibernate: update test.t1 set date=?, some_field=? where id=?
Hibernate: select t1x0_.id as id1_0_, t1x0_.date as date2_0_, t1x0_.some_field as some_fie3_0_ from test.t1 t1x0_ where t1x0_.some_field=?
2017-03-20 17:51:54.194  INFO 74789 --- [           main] hello.T1Service                          : find took: 17 milliseconds
2017-03-20 17:51:54.194  INFO 74789 --- [           main] hello.T1Service                          : t1 not found
2017-03-20 17:51:54.195  INFO 74789 --- [           main] hello.T1Service                          : save took: 1 milliseconds
2017-03-20 17:51:54.195  INFO 74789 --- [           main] hello.T1Service                          : !!! 2th item finished
2017-03-20 17:51:54.195  INFO 74789 --- [           main] hello.T1Service                          : ====================================
2017-03-20 17:51:54.195  INFO 74789 --- [           main] hello.T1Service                          : !!! 3th item start
Hibernate: insert into test.t1 (date, some_field, id) values (?, ?, ?)
Hibernate: update test.t1 set date=?, some_field=? where id=?
Hibernate: update test.t1 set date=?, some_field=? where id=?
Hibernate: select t1x0_.id as id1_0_, t1x0_.date as date2_0_, t1x0_.some_field as some_fie3_0_ from test.t1 t1x0_ where t1x0_.some_field=?
2017-03-20 17:51:54.200  INFO 74789 --- [           main] hello.T1Service                          : find took: 4 milliseconds
2017-03-20 17:51:54.200  INFO 74789 --- [           main] hello.T1Service                          : t1 not found
2017-03-20 17:51:54.200  INFO 74789 --- [           main] hello.T1Service                          : save took: 0 milliseconds
2017-03-20 17:51:54.200  INFO 74789 --- [           main] hello.T1Service                          : !!! 3th item finished
2017-03-20 17:51:54.200  INFO 74789 --- [           main] hello.T1Service                          : ====================================
2017-03-20 17:51:54.200  INFO 74789 --- [           main] hello.T1Service                          : !!! 4th item start
Hibernate: insert into test.t1 (date, some_field, id) values (?, ?, ?)
Hibernate: update test.t1 set date=?, some_field=? where id=?
Hibernate: update test.t1 set date=?, some_field=? where id=?
Hibernate: update test.t1 set date=?, some_field=? where id=?
Hibernate: select t1x0_.id as id1_0_, t1x0_.date as date2_0_, t1x0_.some_field as some_fie3_0_ from test.t1 t1x0_ where t1x0_.some_field=?
2017-03-20 17:51:54.209  INFO 74789 --- [           main] hello.T1Service                          : find took: 9 milliseconds
2017-03-20 17:51:54.209  INFO 74789 --- [           main] hello.T1Service                          : t1 not found
2017-03-20 17:51:54.210  INFO 74789 --- [           main] hello.T1Service                          : save took: 1 milliseconds
2017-03-20 17:51:54.210  INFO 74789 --- [           main] hello.T1Service                          : !!! 4th item finished
2017-03-20 17:51:54.210  INFO 74789 --- [           main] hello.T1Service                          : ====================================

从日志中可以看到，hibernate会生成越来越多的更新语句。

看起来更新语句的数量总是与 T1 等待提交的行数相同。

现在如果我移除转换器，这个问题就会消失。

我可以用hibernate-java8 lib代替这个转换器来达到同样的效果，但是为什么会这样呢？

为什么JPA AttributeConverter 让hibernate 在事务中对整个表生成更新语句？

【问题讨论】：

一切都在一个事务中，每个对象都被添加到一级缓存中。在执行查询之前，hibernate 会对一级缓存中的所有对象进行脏检查。由于属性转换器，它会检测到字段上的更改（出于某种原因），因此需要在执行查询之前对其进行更新。随着一级缓存中项目数量的增加，更新的数量也在增加。
@M.Deinum 说得通。但我仍然对为什么休眠会将数据识别为脏数据感到困惑。自创建以来，日期从未更改。
我怀疑由于转换器的性质，hibernate 提供了默认的转换器（5.2 默认支持此功能，无需创建转换器或使用 hibernate-java8 库）。特定于休眠的一个比您在此处显示的那个更详细。这也是为什么使用默认类型而不是转换器时错误消失的原因。

标签： java spring hibernate jpa spring-data-jpa

【解决方案1】：

我通过在 getter 和 setter 方法中应用转换器而不是作为注释解决了这个问题。像这样：

@Entity
@Table(name = "t1", schema = "test")
public class T1 extends BaseEntity {

  @Column(nullable = false)
  private UUID someField;

  @Column()
  private Timestamp date;

  public T1(UUID someField, ZonedDateTime date) {
    this.someField = someField;
    this.date = date;
  }

    public void setDate(ZonedDateTime date) {
        this.date = new ZonedDateTimeAttributeConverter().convertToDatabaseColumn(date);
    }

    public ZonedDateTime getDate() {
        return new ZonedDateTimeAttributeConverter().convertToEntityAttribute(date);
    }
}

【讨论】：