如何在辅助表中的非主键列上联接表?
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)
回答:
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。
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