有没有办法使用带有前缀的@GeneratedValue 创建字符串序列？

Question

我想创建一个带有前缀“CID_00001”的序列（示例）：

@Id
@GeneratedValue(strategy=GenerationType.SEQUENCE)   
private String id;

有没有办法做到这一点？

Answer 1

您可以使用自定义 id 生成器来做到这一点。

最简单的方法是扩展 Hibernate 的SequenceStyleGenerator，它实现了对数据库序列的访问（包括一些有趣的优化）

public class StringPrefixedSequenceIdGenerator extends SequenceStyleGenerator {

    public static final String VALUE_PREFIX_PARAMETER = "valuePrefix";
    public static final String VALUE_PREFIX_DEFAULT = "";
    private String valuePrefix;

    public static final String NUMBER_FORMAT_PARAMETER = "numberFormat";
    public static final String NUMBER_FORMAT_DEFAULT = "%d";
    private String numberFormat;

    @Override
    public Serializable generate(SharedSessionContractImplementor session, Object object) throws HibernateException {
        return valuePrefix + String.format(numberFormat, super.generate(session, object));
    }

    @Override
    public void configure(Type type, Properties params, ServiceRegistry serviceRegistry) throws MappingException {
        super.configure(LongType.INSTANCE, params, serviceRegistry);
        valuePrefix = ConfigurationHelper.getString(VALUE_PREFIX_PARAMETER, params, VALUE_PREFIX_DEFAULT);
    numberFormat = ConfigurationHelper.getString(NUMBER_FORMAT_PARAMETER, params, NUMBER_FORMAT_DEFAULT);
    }
}

实现自己的 id 生成器后，您可以在@GenericGenerator注释中引用它。

@Entity
public class Book {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "book_seq")
    @GenericGenerator(
        name = "book_seq", 
        strategy = "org.thoughts.on.java.generators.StringPrefixedSequenceIdGenerator", 
        parameters = {
            @Parameter(name = StringPrefixedSequenceIdGenerator.INCREMENT_PARAM, value = "50"),
            @Parameter(name = StringPrefixedSequenceIdGenerator.VALUE_PREFIX_PARAMETER, value = "CID_"),
            @Parameter(name = StringPrefixedSequenceIdGenerator.NUMBER_FORMAT_PARAMETER, value = "%05d") })
    private String id;

    ...
}