JPQL - Joins - MultipleTables和空ResultList

Question

我在JPQL语言中查询了5个表，但如果其中一个表为NULL，则整个查询将失败，resultList为空，并抛出异常。另一方面，如果不是所有的表都包含null，它就会按预期工作。

如何实现返回所有table不为null的对象和null为null的对象？所以我会得到- Object1[]，null，例如...不仅结果列表是空的。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";
    }

Answer 1

使用LEFT JOIN而不是JOIN。缺省情况下，JPQL join是INNER JOINs。