H2索引名称唯一性 | H2索引名称唯一性

本文介绍了H2索引名称唯一性的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我对h2数据库中索引名称的唯一性有一个小问题.使用mysql/mariadb，可以同时为表A和表B定义名为"X"的索引.对于h2数据库，这是不可能的，因为索引的名称在每个数据库中都应该是唯一的.

I have a small problem with the uniqueness of index names in h2 database. With mysql/mariadb it is possible to define index named "X" for table A and table B at the same time. With h2 database it is not possible, since name of the index should be unique per database.

这对我来说是个问题，因为我有一个定义了以下属性的基本JPA实体类:

It is a problem for me, since I have a base JPA entity class with the following property defined:

@org.hibernate.annotations.Index(name = "X")
protected String x;

它被类A和B继承，并且类B的索引创建失败，并出现以下错误:

It is inherited by class A and B and index creation fails for class B with the following error:

ERROR [main] o.h.tool.hbm2ddl.SchemaUpdate   - HHH000388: Unsuccessful: create index X on B(x)
ERROR [main] o.h.tool.hbm2ddl.SchemaUpdate   - Index "X" already exists

是否可以告诉hibernate自动创建索引名称，或者以某种方式为H2创建一个适配器，该适配器将在表名称的前面添加此类索引名称?

Is it possible to tell hibernate to automatically create index name or somehow create an adapter for H2 that will prefix such index names with table names?

推荐答案

尽管您应该始终使用数据库驱动架构演变，并使用FlywayDB迁移架构版本，您可以根据需要覆盖@Index.

Although you should always have the database drive the schema evolution and use FlywayDB to migrate schema versions, you can override the @Index as you want.

我添加了在GitHub上进行测试以证明这一点.

I added a test on GitHub to prove this.

这些类如下:

@Entity(name = "Base")
@Table(name="Base")
@Inheritance(strategy = InheritanceType.JOINED)
public static abstract class Base {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Transient
    protected String x;

    public Long getId() {
        return id;
    }

    public String getX() {
        return x;
    }

    public void setX(String x) {
        this.x = x;
    }
}

@Entity(name = "ChildY")
@Table(name="ChildY")
@DiscriminatorValue("Y")
public static class ChildY extends Base {

    private String y;

    @Override
    @org.hibernate.annotations.Index(name = "xy")
    @Access(AccessType.PROPERTY)
    public String getX() {
        return x;
    }
}

@Entity(name = "ChildZ")
@Table(name="ChildZ")
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorValue("Z")
public static class ChildZ extends Base {

    private String z;

    @Override
    @org.hibernate.annotations.Index(name = "xz")
    @Access(AccessType.PROPERTY)
    public String getX() {
        return x;
    }
}

模式是这样生成的:

create table Base (id bigint generated by default as identity (start with 1), primary key (id))
create table ChildY (x varchar(255), y varchar(255), id bigint not null, primary key (id))
create table ChildZ (x varchar(255), z varchar(255), id bigint not null, primary key (id))
create index xy on ChildY (x)
create index xz on ChildZ (x)

这种方式:

您将在域模型(字段，getter和setter)中保留基类属性
每个表都有自己的带有关联索引的x列

问题是您不能在基类中包含该字段，因为Hibernate会尝试创建该字段两次.您可以在Hibernate上提交一个Jira问题，并提及如果已创建了HBM模式，则应该跳过该索引.

The problem is that you can't have the field in the base class, as Hibernate will attempt to create it twice. You can file a Jira issue on Hibernate and mention that the HBM schema generation should skip the index if it's already created.

最优雅的解决方案是仅使用适当的数据库架构并删除HBM-DDL架构生成.

The most elegant solution is to simply use a proper database schema and remove the HBM-DDL schema generation.

这篇关于H2索引名称唯一性的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！