JPA主键自动生成策略-数据库Oracle

@Target({METHOD, FIELD})
@Retention(RUNTIME)
public @interface GeneratedValue {

    GenerationType strategy() default AUTO;

    String generator() default "";
}

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public enum GenerationType {

	//表生成: 当你的实体需要一个新的主键时，JPA 将会从这个表中获取下一个可用的主键值。这种方式可以跨不同的数据库平台使用。
    TABLE,
	
	//序列生成: 必须指定SEQ,Oracle、PostgreSQL数据库要指定序列
    SEQUENCE,

	//自增生成: 数据库会自动为主键分配一个唯一的值,MySQL 使用 AUTO_INCREMENT
    IDENTITY,

	//自动选择: 自动选择合适的策略来生成主键,根据底层数据库选择使用IDENTITY、SEQUENCE或TABLE策略
    AUTO
}

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代码例子

Controller

@RestController
public class GeneratedStrategyController {

    @Autowired
    GeneratedStrategyService generatedStrategyService;

    @GetMapping("/strategy")
    public Map<String,String> generatedStrategy(){
    	return generatedStrategyService.generatedStrategy();
    }
	
	@GetMapping("/saveNotId")
    public Map<String,String> saveNotId(){
		return generatedStrategyService.saveNotId();
    }

}

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Dao

public interface InventoryListDao extends JpaRepository<InventoryListEntity, Integer> {


    @Query(value = "SELECT * FROM (select * from inventory_list ORDER BY id DESC) WHERE rownum <= 1", nativeQuery = true)
    InventoryListEntity getLastOne();
}

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各dao对应的entity使用不同的策略标识

Service

== 不同策略的dao接口都将entity指定上id，看执行的结果。==
是用JPA的自带接口方法，执行save时，entity中主键不为空，则会先通过id查询数据。与id为null的情况不同，插入的entity会在原来的对象上修改，不用重新接收对象。如果Entity的id不为null，对应id的数据不存在，则需要重新接收才能获取到对应entity的id值。

@Component
public class GeneratedStrategyServiceImpl implements GeneratedStrategyService {

    @Autowired
    InventoryListDao inventoryListDao;

    @Autowired
    InventoryListAUTODao inventoryListAUTODao;

    @Autowired
    InventoryListSEQUENCEDao inventoryListSEQUENCEDao;

    @Autowired
    InventoryListTABLEDao inventoryListTABLEDao;

    private final Log log = LogFactory.getLog(this.getClass());
    Gson gson = new Gson();

    @Override
    @Transactional
    public Map<String,String> generatedStrategy(){
        Map<String, String> map = new HashMap<>();

        InventoryListEntity source = inventoryListDao.getLastOne();

        log.info("source: " + gson.toJson(source));

        // TABLE
        InventoryListTABLEEntity tableEntity = gson.fromJson(gson.toJson(source), InventoryListTABLEEntity.class);
        log.info("TABLE开始: " + gson.toJson(tableEntity));
        tableEntity.setId(source.getId() + 10);
        InventoryListTABLEEntity saveTableEntity = inventoryListTABLEDao.save(tableEntity);
        log.info("TABLE结束1: " + gson.toJson(tableEntity));
        log.info("TABLE结束2: " + gson.toJson(saveTableEntity));
        map.put("TABLE", String.valueOf(saveTableEntity.getId()));

        // SEQUENCE
        InventoryListSEQUENCEEntity sequenceEntity = gson.fromJson(gson.toJson(source), InventoryListSEQUENCEEntity.class);
        log.info("SEQUENCE开始: " + gson.toJson(sequenceEntity));
        sequenceEntity.setId(source.getId() + 20);
        InventoryListSEQUENCEEntity saveSequenceEntity = inventoryListSEQUENCEDao.save(sequenceEntity);
        log.info("SEQUENCE结束1: " + gson.toJson(sequenceEntity));
        log.info("SEQUENCE结束2: " + gson.toJson(saveSequenceEntity));
        map.put("SEQUENCE", String.valueOf(saveSequenceEntity.getId()));


        // IDENTITY
        InventoryListEntity identityEntity = gson.fromJson(gson.toJson(source), InventoryListEntity.class);
        log.info("IDENTITY开始: " + gson.toJson(identityEntity));
        identityEntity.setId(source.getId() + 30);
        InventoryListEntity saveIdentityEntity = inventoryListDao.save(identityEntity);
        log.info("IDENTITY结束1: " + gson.toJson(identityEntity));
        log.info("IDENTITY结束2: " + gson.toJson(saveIdentityEntity));
        map.put("IDENTITY", String.valueOf(saveIdentityEntity.getId()));

        // AUTO
        InventoryListAUTOEntity autoEntity = gson.fromJson(gson.toJson(source), InventoryListAUTOEntity.class);
        log.info("AUTO开始: " + gson.toJson(autoEntity));
        autoEntity.setId(source.getId() + 40);
        InventoryListAUTOEntity saveAutoEntity = inventoryListAUTODao.save(autoEntity);
        log.info("AUTO结束1: " + gson.toJson(autoEntity));
        log.info("AUTO结束2: " + gson.toJson(saveAutoEntity));
        map.put("AUTO", String.valueOf(saveAutoEntity.getId()));
        
        return map;
    }

    @Override
    public Map<String, String> saveNotId() {
        Map<String, String> map = new HashMap<>();

        InventoryListEntity source = inventoryListDao.getLastOne();

        log.info("source: " + gson.toJson(source));

        InventoryListTABLEEntity tableEntity = gson.fromJson(gson.toJson(source), InventoryListTABLEEntity.class);
        tableEntity.setId(null);

        InventoryListTABLEEntity saveTableEntity = inventoryListTABLEDao.save(tableEntity);
        log.info("TABLE结束1: " + gson.toJson(tableEntity));
        log.info("TABLE结束2: " + gson.toJson(saveTableEntity));
        map.put("TABLE", String.valueOf(saveTableEntity.getId()));
        
        return map;
    }
}

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策略使用错误提示

TABLE

== 不指定从表中查询一些数据==

SEQUENCE

不指定generator，默认为hibernate_sequence。

IDENTITY

直接往数据库中插入数据，出现不为空插入数据错误

AUTO

SequenceGenerator

@Repeatable(SequenceGenerators.class)
@Target({TYPE, METHOD, FIELD}) 
@Retention(RUNTIME)
public @interface SequenceGenerator {
	// 与GeneratedValue连用指定自增序列名称
    String name();
	// 数据库对应自增序列名称
    String sequenceName() default "";

    String catalog() default "";

    String schema() default "";

    int initialValue() default 1;

    int allocationSize() default 50;
}

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GeneratedValue指定自增序列和SequenceGenerator的name不一致，优先级高(不一致序列,GeneratedValue优先级更高)
序列不对的时候，启动会变慢(我的本地启动是这样)