@OneToMany关系属性未填充

Question

我已经实现了 join, Multiple Table Inheritance。

有一个'父'表pois和两个子表:xPois和yPois，然后我有一个抽象的PoiDao类以及XPoiDao和YPoiDao类扩展PoiDao。

一个poi可以有多个预订，但一个预订只属于一个poi。

子表dao中定义的命名查询可以很好地处理在各自(直接)表层次结构中定义的属性。父表与另一个名为reservations的表有一个外键关系(表reservations保存表pois的外键)。问题是这个reservations表中的记录没有被提取。

在MySql Workbench中运行此SQL语句将得到所需的结果集:

SELECT * FROM xPois pp 
    LEFT JOIN pois p ON pp.poiId = p.poiId 
    LEFT JOIN reservations r ON p.poiId = r.poiId 
    WHERE pp.xPoiId = '2011';

在Eclipse中，我可以看到{IndirectList: not instantiated}当我在调试模式下检查xDao实例时。

如何使用JPA从存储在PoiDao中的表中获取记录?

public abstract class PoiDao implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="poiId")
    private Integer poiId;
    @OneToOne(optional=false, cascade=CascadeType.ALL)
    @JoinColumn(name="addressId",insertable=true,
    updatable=true, unique=true, nullable=false)
    private AddressDao address;
    @Embedded
    private GeoLocationDao geoLocation;
    @Convert("poiTypeConverter")
    private ServiceTypeEnum poiType;
    @Column(name="operator")
    private String operator;
    @Column(name="reservable")
    private boolean reservable;
    @OneToMany(orphanRemoval=true, cascade=CascadeType.ALL, fetch=FetchType.LAZY)
    @JoinColumn(name="poiId", insertable=true, updatable=true)
    private List<ReservationDao>    existingReservations;
    ...
    }
@Entity
@Table(name="xPois")
@DiscriminatorValue("X")
@NamedQueries({
    @NamedQuery(name="XPoiDao.findAll", query="SELECT p FROM XPoiDao p"), 
    @NamedQuery(name="XPoiDao.findByXPoiId", 
                query="SELECT pp FROM XPoiDao pp LEFT JOIN PoiDao p ON pp.poiId = p.poiId "
                        + "LEFT JOIN ReservationDao r ON p.poiId = r.poiId WHERE pp.xPoiId = :xPoiId")
})
@ObjectTypeConverters({
    @ObjectTypeConverter (
            name="xPoiStatusConverter",
            dataType=java.lang.String.class,        // type in DB
            objectType=XPoiStatusEnum.class,    // Java type
            conversionValues={
                @ConversionValue(dataValue="FREE", objectValue="FREE"),
                @ConversionValue(dataValue="OCCUPIED BY VALUE", objectValue="OCCUPIED_BY_VALUE"),
                @ConversionValue(dataValue="OCCUPIED MANUALLY", objectValue="OCCUPIED_MANUALLY"),
                @ConversionValue(dataValue="BLOCKED", objectValue="BLOCKED")
            }
    )
})
public class XPoiDao extends PoiDao implements Serializable {
    /**
     * 
     */
    private static final long serialVersionUID = 2496267921294255723L;
//  @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="id")
    private Integer             id;
    @Column(name="xPoiId")
    private String              xPoiId;
    @Convert("xPoiStatusConverter")
    @Column(name="status")
    private XPoiStatusEnum status;
    @Embedded
    private ContactDao          contact;
//  @OneToMany(orphanRemoval=true, cascade=CascadeType.ALL, fetch=FetchType.LAZY)
//  @JoinColumn(name="poiId",insertable=true,updatable=true)
//  private List<ReservationDao>    existingReservations;
    @OneToMany(orphanRemoval=true, cascade=CascadeType.ALL, fetch=FetchType.LAZY)
    @JoinColumn(name="parkingPoiId",insertable=true,updatable=true)
    private List<OperatingHourDao> operatingHours;
    ...
    }

Answer 1

这里有FetchType.LAZY。当你试图访问它时，你得到一个空列表吗?调试器可能不会触发获取请求。