Hibernate @EmbeddedId + join

Question

我有一个休眠映射问题.我有以下两个DB表(我不允许更改DB):

LOCATIONS {
   ID, -- PK
   NAME
}

LOCATION_GROUPS {
   LOC_ID, -- PK, and FK to LOCATIONS.ID
   GROUP_NAME -- PK
}

我试图为这些数据库表创建实体,但我不知道如何映射表之间的连接.这是我的尝试(但这是错的):

@Embeddable
public class LocationGroupId implements Serializable {

    private static final long serialVersionUID = -6437671620548733621L;
    private Location loc;  
    private String group;   

    @Column(name = "LOC_ID")
    public Location getLoc() {
        return loc;
    }

    @Column(name = "GROUP_NAME")
    public String getGroup() {
        return group;
    }

    // ...
}   

@Entity
@Table(name = "LOCATION_GROUPS")
public class LocationGroup {

    private LocationGroupId id;

    @EmbeddedId
    public LocationGroupId getId() {
        return id;
    }

    // ...
}


@Entity
@Table(name = "LOCATIONS")
public class Location {

    private Long id;
    private String name;
    private List<LocationGroup> groups;

    @Column(name = "NAME")
    public String getName() {
        return this.name;
    }

    @OneToMany(mappedBy = "id.loc")
    public List<LocationGroup> getGroups() {
        return this.groups;
    }

    @Id
    @Column(name = "ID")
    @SequenceGenerator(name = "LocationIdGen", sequenceName = "LOCATION_SQ")
    @GeneratedValue(strategy = GenerationType.AUTO, generator = "LocationIdGen")
    public Long getId() {
        return this.id;
    }

    // ...
}

困难在于我想在列和embeddedId列的一部分之间建立OneToMany连接.对这个问题有什么想法吗？(我正在使用hibernate 4.0.1)

Answer 1

该位置必须映射@JoinColumn,而不是@Column:

@JoinColumn(name = "LOC_ID")
public Location getLoc() {
    return loc;
}

请注意,这不是标准的JPA.为了使它成为标准,你会使用

@Embeddable
public class LocationGroupId implements Serializable {

    private static final long serialVersionUID = -6437671620548733621L;
    private Long locationId;  
    private String group;   

    @Column(name = "LOC_ID")
    public Long getLocationId() {
        return loc;
    }

    @Column(name = "GROUP_NAME")
    public String getGroup() {
        return group;
    }

    // ...
}   

@Entity
@Table(name = "LOCATION_GROUPS")
public class LocationGroup {

    private LocationGroupId id;
    private Location location;

    @EmbeddedId
    public LocationGroupId getId() {
        return id;
    }

    @ManyToOne
    @JoinColumn(name = "LOC_ID")
    @MapsId("locationId")
    private Location getLocation() {
        return location;
    }

    // ...
}

这两个映射在文档中进行了解释.