休眠@EmbeddedId +加入

Question

我有一个hibernate映射问题。我有以下两个数据库表（不允许更改数据库）：

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，但是我不知道如何映射表之间的连接。这是我的尝试（但这是错误的）：

@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一部分嵌入式Id列之间建立一个OneToMany连接。对这个问题有想法吗？（我正在使用hibernate4.0.1）

Answer 1

必须使用@JoinColumn而不是使用来映射位置@Column：

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

请注意，虽然这不是标准的JPA。要使其成为标准，您将使用

@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;
    }

    // ...
}

在文档中解释了这两个映射。