java - JPA/Hibernate 如何将特定字段从一个实体连接到另一个实体

Question

假设我们有实体 A 和实体 B，每个实体都有其对应的表 A 和 B。

实体 A 是一家酒店，拥有 ID 和多个字段，例如国家/地区、城市、邮政编码等。

实体 B 是一个描述列表，有一个 ID(与实体 A 中的 ID 相同)和另外 2 个字段:语言和描述。

我在我的 DAO 中进行以下查询:

    Query query = getEntityManager().createQuery("FROM " + type.getSimpleName() +
            " WHERE City = :cityParam AND Country = :countryParam");
    query.setParameter("cityParam", cityParam);
    query.setParameter("countryParam", countryNameParam);
    query.setMaxResults(numberOfResults);
    List<HotelDto> hotelMap = query.getResultList();
    ListResponseModel result = new ListResponseModel();
    result.setHotelMap(hotelMap);
    return result.getHotelMap().size() > 0 ? result : null;

实体 A，酒店实体如下所示:

@Entity
@Table(name = "propertyList", uniqueConstraints = 
{ @UniqueConstraint(columnNames = "HotelID")})
public class Hotel implements Serializable, EntityWithId<Long> {
private static final long serialVersionUID = 1L;

@Id
@GeneratedValue
@Column(name = "HotelID")
private Long hotelId;

@Column(name = "Name")
private String name;

@Column(name = "Address")
private String address;

@Column(name = "City")
private String city;

@Column(name = "StateProvince")
private String stateProvince;

@Column(name = "PostalCode")
private String postalCode;

@Column(name = "Country")
private String country;

@OneToOne(fetch = FetchType.LAZY)
@PrimaryKeyJoinColumn(name = "propertyhotelid")
private PropertyDescription propertyDescription;
[...]

实体 B(描述)如下所示:

@Entity
@Table(name = "propertyDescriptionList", uniqueConstraints = 
{ @UniqueConstraint(columnNames = "HotelID")})
public class PropertyDescription implements Serializable, EntityWithId<Long> {

private static final long serialVersionUID = 1L;

@Id
@Column(name = "HotelID", unique = true, nullable = false)
private Long hotelId;

@Column(name = "PropertyDescription")
private String propertyDescription;

问题是，一旦我获得结果集，单个实体将如下所示:

hotelId: 124125,
name: "Random Hotel",
address: "Some Address",
city: "Shambala",
postalCode: "W2 3NA",
country: "Nevereverland",
-propertyDescription: {
    hotelId: 105496,
    propertyDescription: "Insert Description here bla bla bla."
}
}

我想要得到的是这样的:

hotelId: 124125,
name: "Random Hotel",
address: "Some Address",
city: "Shambala",
postalCode: "W2 3NA",
country: "Nevereverland",
propertyDescription: "Insert Description here bla bla bla."
}

因为我只对作为字符串的描述本身感兴趣，而不是对也具有 ID 的整个对象(重复)感兴趣。

实现这一目标的最佳方法是什么？

Answer 1

从你的问题来看，听起来你正在寻找一种将两个表映射到一个实体的方法？如果是这样，您可以使用 @SecondaryTable 执行此操作:字符串“描述”将简单地成为您的酒店实体的一个字段。

@Entity
@Table(name = "propertyList", uniqueConstraints = { @UniqueConstraint(columnNames = "HotelID") })
@SecondaryTable(name = "propertyDescriptionList", pkJoinColumns = @PrimaryKeyJoinColumn(name = "HotelID"), uniqueConstraints = { @UniqueConstraint(columnNames = "HotelID") })
public class Hotel implements Serializable {

    @Id
    @Column(name = "HotelID")
    private Long hotelId;

    @Column(name = "PropertyDescription", table = "propertyDescriptionList")
    private String propertyDescription;

}