JPA ID是连续的吗 [英] Are JPA Ids sequential

问题描述

播放框架会为实体创建一个ID，从而将模型类扩展如下:

Play framework creates an Id for Entities which extend the model class as such:

@MappedSuperclass
public class Model extends GenericModel {

    @Id
    @GeneratedValue
    public Long id;

    public Long getId() {
        return id;
    }

    @Override
    public Object _key() {
        return getId();
    }

}

是否可以使用此ID(最大ID)来确定最近创建的记录?

Is it possible to use this id (max id) to determine the latest created record?

在发生故障的情况下，我想使某些作业从某个角度重新运行，这是迄今为止添加此功能的最简单方法.

I want to make some jobs rerunnable from a certain point in the event of failures and this would be by far the easiest way to add this functionality.

我不想添加创建时间列，因为表已经很大.

I do not want to add a creation time column as the table is already huge.

推荐答案

@GeneratedValue的默认strategy()是GenerationType.AUTO.定义是

指示持久性提供程序应为特定数据库选择适当的策略. AUTO生成策略可能期望数据库资源存在，或者可能尝试创建一个数据库资源.如果供应商不支持架构生成或无法在运行时创建架构资源，则供应商可能会提供有关如何创建此类资源的文档.

Indicates that the persistence provider should pick an appropriate strategy for the particular database. The AUTO generation strategy may expect a database resource to exist, or it may attempt to create one. A vendor may provide documentation on how to create such resources in the event that it does not support schema generation or cannot create the schema resource at runtime.

因此，这取决于您使用的数据库.如果使用GenerationType.IDENTITY，则某些数据库供应商将使用某种"auto_increment"值.至少对于MySQL来说是这样.如果将MySQL与GenerationType.IDENTITY结合使用，则可以使用max(id)确定最新创建的记录.有关更多信息，我将检查您的数据库规格.

So it depends on the database you use. If you use GenerationType.IDENTITY, some database vendors use some kind of "auto_increment" value. At least, this is true for MySQL. If you use MySQL with GenerationType.IDENTITY you can use max(id) to determine the latest created record. For further information, I'd check your database spec.

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