JPQL - 连接 - MultipleTables 和空 ResultList

Posted 2023-02-26

【中文标题】JPQL - 连接 - MultipleTables 和空 ResultList

【英文标题】：JPQL - Joins - MultipleTables and empty ResultList

【发布时间】：2018-10-10 21:37:05

【问题描述】：

我在 JPQL 中通过 5 个表进行了查询，但如果其中一个表为 NULL，则整个查询失败并且 resultList 为空并引发异常。另一方面，如果所有表都不包含 null，则它按预期工作。

如何实现它以返回所有表不为空的对象和为空的对象为空？所以我会得到 - Object1[], null, null, null 例如......而不仅仅是空的结果列表...... 非常感谢:)

public List<Object[]> getAdditionalInformation(String ppin) 
    Query query = em.createQuery("SELECT p, pl, r, d, do FROM Patient p JOIN p.placements pl JOIN pl.room r"
            + " JOIN r.department d JOIN d.doctors do where p.pin = :ppin");
    query.setParameter("ppin", ppin);

    return query.getResultList();


@Transactional
    public AdditionalPD getAdditional(String ppin) 
        List<Object[]> list = hr.getAdditionalInformation(ppin);

        AdditionalPD adp = new AdditionalPD();
        Patient patient = null;
        Placement placement = null;
        Room room = null;
        Department department = null;
        Doctor doctor = null;

        for(Object[] object : list) 
            patient = (Patient) object[0];
            placement = (Placement) object[1];
            room = (Room) object[2];
            department = (Department) object[3];
            doctor = (Doctor) object[4];
        

        adp.setPatientFirstName(patient.getFirstName());
        adp.setPatientLastName(patient.getLastName());
        adp.setAge(countAge(ppin));
        adp.setFrom(placement.getFrom());
        adp.setTo(placement.getTo());
        adp.setRoomName(room.getName());
        adp.setDepartmentName(department.getName());
        adp.setDoctorFirstName(doctor.getFirstName());
        adp.setDoctorLastName(doctor.getLastName());

        return adp;
    

@GetMapping("/additional/pin/ppin")
    public String additionalInformation(@PathVariable String ppin, Model model) 

        AdditionalPD adp = has.getAdditional(ppin);

        model.addAttribute("adp", adp);

        return "additional";
    

【问题讨论】：

见What should I do when someone answers my question?

【参考方案1】：

使用LEFT JOIN 代替JOIN。 JPQL 连接默认为INNER JOINs。