Spring Data JPA @Query - 选择最大值

Question

我正在尝试使用select max和where与@Query编写查询

以下不起作用，我该如何解决？

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;

@Repository
interface IntermediateInvoiceRepository extends JpaRepository<Invoice, String> {

@Query("SELECT max(i.sequence) " +
        "FROM Invoice as i " +
        "WHERE i.fleetId = :fleetId" +
        "   AND i.sequence IS NOT NULL")
Long findMaxSequence(@Param("fleetId") String fleetId);

}

我遇到了另一个答案，但它明确地使用了实体管理器，它不一样

How do I write a MAX query with a where clause in JPA 2.0?

错误是：

2018-09-14T09:27:57,180Z  [main] ERROR o.s.boot.SpringApplication     - Application startup failed
org.springframework.data.mapping.PropertyReferenceException: No property findMaxSequence found for type Invoice!

发票类（为简洁而简化）：

@Entity
@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
@Table(name = "invoices", indexes = {
        @Index(name = "IDX_FLEET", columnList = "fleetId", unique = false)
        ,
        @Index(name = "IDX_USERSSS", columnList = "userId", unique = false)
        ,
        @Index(name = "IDX_TIME", columnList = "invoiceDate", unique = false)
        ,
        @Index(name = "IDX_SEQUENCE", columnList = "sequence", unique = false)
})
@JsonIgnoreProperties(ignoreUnknown = true)
public class Invoice implements Serializable {

    private static final long serialVersionUID = 1L;

    @GeneratedValue(generator = "uuid")
    @GenericGenerator(name = "uuid", strategy = "uuid2")
    @Column(columnDefinition = "CHAR(36)")
    @Id
    private String id;

    @Column
    private long sequence;

...

更新：

• 也许在序列列上使用带有DESC排序的findOne进行解决？ @Query（“SELECT i.sequence”+“FROM Invoice as i”+“WHERE i.fleetId =：fleetId”+“ORDER BY i.sequence DESC”）long getMaxSequence（@Param（“fleetId”）String fleetId）;

但我需要以某种方式将结果集限制为1

更新2：

修复import org.springframework.data.jpa.repository.Query;仍然是错误的

Answer 1

我找到了一个解决方法：

创建一个简单的存储库方法返回Page并接受Pageable：

Page<Invoice> findByFleetId(String fleetId, Pageable pageable);

这样我们可以通过以下方式模仿ORDER BY sequence LIMIT 1：

long maxNewSeq = 0;
PageRequest pageRequest = new PageRequest(0, 1, Sort.Direction.DESC, "sequence");
Page<Invoice> pageableInvoices = invoiceRepository.findByFleetId(invoice.getFleetId(), pageRequest);
if(pageableInvoices.getTotalElements() > 0){
    maxNewSeq = pageableInvoices.getContent().get(0).getSequence();
}

invoice.setSequence(Math.max(0, maxNewSeq) + 1);

似乎像魅力一样工作。

Answer 2

由于您使用的是JPA存储库，请使用：

org.springframework.data.jpa.repository.Query

注释而不是

org.springframework.data.mongodb.repository.Query

您可以创建查询方法，而无需使用@Query注释，例如：

Invoice findFirstByFleetIdOrderBySequenceDesc（String fleetId）;

返回您需要的发票。