mysql - 选择最大 native 查询 hibernate

Question

我正在尝试使用带有 @Query 注释的 native 查询来获取表中列的最大值

我尝试从这里的示例中得出它:https://www.baeldung.com/spring-data-jpa-query

 @Query(value = "SELECT max(i.sequence) " +
            "FROM invoices as i " +
            "WHERE i.fleet_id = ?1", nativeQuery = true)
    Long findMaxSequence(String fleetId);

我也尝试过:

@Query(value = "SELECT max(i.sequence) " +
        "FROM invoices as i " +
        "WHERE i.fleet_id = :fleetId", nativeQuery = true)
Long findMaxSequence(@Param("fleetId") String fleetId);

当我将我的方法称为:

long maxSeq = invoiceRepository.findMaxSequenceForFleetId(invoice.getFleetId());

我收到一个NullPointerException。有什么想法吗？

Invoice 实体如下所示:

@Entity
@Table(name = "invoices"}
public class Invoice implements Serializable {


    @Id
    private String id;

    @Column
    private long sequence;

    @Column(length = 12)
    private String fleetId;

    // ...
}

Answer 1

该问题是由于数据库为空，因此查询返回 null

和基本类型(例如long)不能分配给空值。奇怪的是编译器没有提示..

我修改了我的代码如下:

Long maxSeq = invoiceRepository.findMaxSequenceForFleetId(invoice.getFleetId());
if(maxSeq == null){
    maxSeq = 0L;
}