休眠生成器增量句柄如何删除 [英] how does hibernate generator increment handle deletes

问题描述

这就是我使用发电机的方式:

This is how i am using the generator:

    <id name="id" column="column_name">
        <generator class="increment"/>
    </id>

private Integer id;

我看到的行为是:

1. 创建第一个对象
2. 休眠分配id = 1
3. 删除该对象
4. 关闭服务器并重新启动它(答案后添加了此内容)
5. 创建第二个对象
6. 休眠分配id = 1

注意:我希望新的数字是2，即使1不再存在.

note: I expected the new number to be 2, even though 1 doesnt exist anymore.

我仅使用HSQLDB对此进行了测试.

I have only tested this using HSQLDB.

问题:这是预期的行为吗?

Question: Is this expected behaviour?

源中的AFAICT，下一个数字应为2

AFAICT in the source, the next number should be 2 https://github.com/hibernate/hibernate-core/blob/master/hibernate-core/src/main/java/org/hibernate/id/IncrementGenerator.java#L68

更新:根据Ralph的回答，如果我跳过第4步(不要关闭服务器)，则它会正确递增.这是因为在启动时将该值设置为max(id)，然后将其存储在内存中.

Update: As per Ralph's answer, if I skip step 4 (dont shut down the server), it increments correctly. Its because the value gets set to max(id) on start up, and stored in memory after that.

推荐答案

IncrementGenerator用"select max(" + column + ") from " + buf.toString();初始化，其中column是ID列.

The IncrementGenerator is initialized with "select max(" + column + ") from " + buf.toString(); where column is the ID column.

这意味着每次创建新的IncrementGenerator时(更精确:在调用configure之后第一次调用generate)，id计数器将从数据库中重置"为最大值.

This means every time a new IncrementGenerator is created (more precise: the first time generate is invoked after configure is invoked) the id counter will be "reseted" to the max value from the DB.

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