一对多关系中的实体仅在应用程序重新启动后可见（JPA和PostgreSQL）

Question

I have a problem with entity relationships using the JPA.

I have these two JPA Entities. Both tables are created by the application when the application boots up using <property name="javax.persistence.schema-generation.database.action" value="drop-and-create"/>

@Entity(name = "patient")
public class Patient {

    @XmlID
    @XmlElement
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", updatable = false, nullable = false)
    private Integer id;

    private Integer height;

    private Integer weight;

    @XmlJavaTypeAdapter(YearAdapter.class)
    @Temporal(TemporalType.TIMESTAMP)
    private Date yearOfBirth;

    private Sex sex;

    @OneToMany(mappedBy = "patient", fetch = FetchType.LAZY)
    private List<Sample> samples;

   // Getters and Setters omitted
}

@Entity(name = "sample")
public class Sample {

    @XmlID
    @XmlElement
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", updatable = false, nullable = false)
    private Integer id;

    private boolean aliquotated;

    private BigDecimal initialVolume;

    private BigDecimal availableVolume;

    @XmlIDREF
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "patient_id")
    private Patient patient;

   // Getters and Setters omitted
}

When adding new Samples using these two methods

@PersistenceContext(unitName = "postgres-hcc")
private EntityManager em;

/* ... */

@Transactional
public Sample storeSample(Sample sample) {

    sample.setAvailableVolume(sample.getInitialVolume());

    em.persist(sample);

    return sample;
}

@Transactional
public Sample storeSample(SampleDTO sampleDTO) {

    Sample sample = new Sample();

    sample.setInitialVolume(sampleDTO.getInitialVolume());
    sample.setAliquotated(sampleDTO.isAliquotated());
    sample.setPatient(patientService.getPatient(sampleDTO.getPatientId()));

    return this.storeSample(sample);
}

new samples are not visible when fetching Patients; the samples List is empty. They are written to the database though. Also, after restarting the application without the drop-and-create option, all samples (that were written to the DB) become visible in the samples list.

I have a feeling this has to do with how the linked Samples are fetched and are not re-fetched once new Samples are added to a patient. Hence they appear after the application restarts.

Is there anything that can be done in this case or are significant changes required?

---

ADDITIONAL INFO Fetching the patient(s):

public List<Patient> getPatients() {
    TypedQuery<Patient> q = em.createQuery("SELECT p FROM patient p", Patient.class);

    if (q == null) {
        return null;
    }

    return q.getResultList();
}

public Patient getPatient(Integer patientId) {
    Patient patient = em.find(Patient.class, patientId);

    if (patient != null) {
        return patient;
    } else {
        throw new NotFoundException("No patient with id " + patientId);
    }
}

Answer 1

There is no such thing as automatic re-fetch.

You must add the Sample to the Patient not only the Patient to the sample.