如何在辅助表中的非主键列上联接表？

Question

我遇到一种情况，我需要在ORM类层次结构中的对象上联接表，其中join列不是基类的主键。这是表格设计的示例：

CREATE TABLE APP.FOO
(
    FOO_ID INTEGER NOT NULL,
    TYPE_ID INTEGER NOT NULL,
    PRIMARY KEY( FOO_ID )
)

CREATE TABLE APP.BAR
(
    FOO_ID INTEGER NOT NULL,
    BAR_ID INTEGER NOT NULL,
    PRIMARY KEY( BAR_ID ),
    CONSTRAINT bar_fk FOREIGN KEY( FOO_ID ) REFERENCES APP.FOO( FOO_ID )
)

CREATE TABLE APP.BAR_NAMES
(
    BAR_ID INTEGER NOT NULL,
    BAR_NAME VARCHAR(128) NOT NULL,
    PRIMARY KEY( BAR_ID, BAR_NAME),
    CONSTRAINT bar_names_fk FOREIGN KEY( BAR_ID ) REFERENCES APP.BAR( BAR_ID )
)

这是映射（为简洁起见，省略了getter和setter方法

@Entity
@Table(name = "FOO")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "TYPE_ID", discriminatorType =    javax.persistence.DiscriminatorType.INTEGER)
public abstract class Foo {
    @Id
    @Column(name = "FOO_ID")
    private Long fooId;
}

@Entity
@DiscriminatorValue("1")
@SecondaryTable(name = "BAR", pkJoinColumns = { @PrimaryKeyJoinColumn(name = "FOO_ID", referencedColumnName = "FOO_ID") })
public class Bar extends Foo{
    @Column(table = "BAR", name = "BAR_ID")
    Long barId;
 }

BAR_NAMES鉴于其连接列不是FOO_ID，我如何添加映射BAR_ID？

我尝试了以下方法：

@CollectionOfElements(fetch = FetchType.LAZY)
@Column(name = "BAR_NAME")
@JoinTable(name = "BAR_NAMES", joinColumns = @JoinColumn(table = "BAR", name = "BAR_ID", referencedColumnName="BAR_ID"))
List<String> names = new ArrayList<String>();

这将失败，因为用于检索Bar对象的SQL试图从FOO表中获取BAR_ID值。我也尝试过将JoinTable注释替换为

@JoinTable(name = "BAR_NAMES", joinColumns = @JoinColumn(name = "BAR_ID"))

这不会产生SQL错误，也不会检索任何数据，因为针对BAR_NAMES的查询使用FOO_ID作为联接值而不是BAR_ID。

为了进行测试，我使用以下命令填充了数据库

insert into FOO (FOO_ID, TYPE_ID) values (10, 1);
insert into BAR (FOO_ID, BAR_ID) values (10, 20);
insert into BAR_NAMES (BAR_ID, BAR_NAME) values (20, 'HELLO');

当获得ID为10的Foo对象时，许多似乎可行的解决方案将返回一个空集合（与包含1个名称的集合相对）

Answer 1

我能够找到解决方案。如果您像这样映射Bar类

@Entity
@DiscriminatorValue("1")
@SecondaryTable(name = "BAR", pkJoinColumns = { @PrimaryKeyJoinColumn(name = "FOO_ID", referencedColumnName = "FOO_ID") })
public class Bar extends Foo {
    @OneToOne
    @JoinColumn(table = "BAR", name = "BAR_ID")
    MiniBar miniBar;
}

并添加以下类

@Entity
@SqlResultSetMapping(name = "compositekey", entities = @EntityResult(entityClass = MiniBar.class, fields = { @FieldResult(name = "miniBar", column = "BAR_ID"), }))
@NamedNativeQuery(name = "compositekey", query = "select BAR_ID from BAR", resultSetMapping = "compositekey")
@Table(name = "BAR")
public class MiniBar {
    @Id
    @Column(name = "BAR_ID")
    Long barId;
}

然后，您可以将想要的任何类型的映射添加到MiniBar类中，就像barId是主键一样，然后进一步使其在外部Bar类中可用。