Sping引导JPA更新失败

Question

JPA存储库更新失败。

following code of service not works. insert works

 sping boot 2.1.7

 @Override
 @Transactional
 public Employee updateEmployee(Employee emp, long id) throws Exception {
    System.out.println("Repository emp" + emp.getPlantModel() + " id " + id);
    // return employeeRepository.save(emp);
    Optional<Employee> employee = employeeRepository.findById(id);
    System.out.println("plant make" + emp.getPlantMake());
    System.out.println("emo is present" + employee.isPresent());
    if (employee.isPresent()) {
        Employee newEntity = employee.get();
        newEntity.setPlantMake(emp.getPlantMake());
        newEntity.setPlantModel(emp.getPlantModel());
        System.out.println("updating employee entity");


        return  employeeRepository.save(newEntity);
    } else {
        return null;
    }

}

插入有效，jpa update引发异常而没有任何重要原因

实体类如下，我已连接到postgresSQL

public class Employee implements Serializable {

private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "emp_id", columnDefinition = "serial")
private long empId;

@Column(name = "plant_make")
private String plantMake;

使用Spring Boot 2.17寻找解决方案