Enterprise Java Development@TOPIC@
Map a single Java class to multiple tables in database
Uses a join of two or more tables and a single Java class
One table is designated as primary
Secondary and primary must have a column to join
Three tables (one primary and two secondary) joined
Figure 5.1. Multi-table Mapping Example Database Schema
create table ORMCORE_WATCH (
id bigint not null,
make varchar(255),
model varchar(255),
primary key (id)
)create table ORMCORE_OWNER (
cardnum varchar(255),
NAME varchar(255),
OWNER_ID bigint not null,
primary key (OWNER_ID)
)create table ORMCORE_MAKER (
address varchar(255),
NAME varchar(255),
phone varchar(255),
MAKER_ID bigint not null,
primary key (MAKER_ID)
)alter table ORMCORE_MAKER
add constraint FKB91D15CEC0CE58E2
foreign key (MAKER_ID)
references ORMCORE_WATCH
alter table ORMCORE_OWNER
add constraint FKB943503D985CE28
foreign key (OWNER_ID)
references ORMCORE_WATCHFigure 5.2. Multi-table Mapping Example Entity Class
@Entity
@Table(name="ORMCORE_WATCH")
@SecondaryTables({
@SecondaryTable(name="ORMCORE_OWNER",
pkJoinColumns={
@PrimaryKeyJoinColumn(name="OWNER_ID")}),
@SecondaryTable(name="ORMCORE_MAKER",
pkJoinColumns={
@PrimaryKeyJoinColumn(name="MAKER_ID")})
})
public class Watch {
@Id
private long id;
private String make;
private String model;
@Column(name="NAME", table="ORMCORE_OWNER")
private String owner;
@Column(table="ORMCORE_OWNER")
private String cardnum;
@Column(name="NAME", table="ORMCORE_MAKER")
private String manufacturer;
@Column(table="ORMCORE_MAKER")
private String address;
@Column(table="ORMCORE_MAKER")
private String phone;
Figure 5.3. Multi-table Mapping Example orm.xml
<entity class="ejava.examples.orm.core.mapped.Watch" access="FIELD">
<table name="ORMCORE_WATCH"/>
<secondary-table name="ORMCORE_OWNER">
<primary-key-join-column name="OWNER_ID"/>
</secondary-table>
<secondary-table name="ORMCORE_MAKER">
<primary-key-join-column name="MAKER_ID"/>
</secondary-table>
<attributes>
<id name="id"/>
<basic name="owner">
<column name="NAME" table="ORMCORE_OWNER"/>
</basic>
<basic name="cardnum">
<column table="ORMCORE_OWNER"/>
</basic>
<basic name="manufacturer">
<column name="NAME" table="ORMCORE_MAKER"/>
</basic>
<basic name="address">
<column table="ORMCORE_MAKER"/>
</basic>
<basic name="phone">
<column table="ORMCORE_MAKER"/>
</basic>
</attributes>
</entity>
Figure 5.4. Multi-table Mapping Example Test
//leave a watch in DB to inspect
Watch watch3 = new Watch(3);
watch3.setMake("ontime3");
watch3.setModel("round-and-round3");
watch3.setOwner("john doe3");
watch3.setCardnum("123-45-67893");
watch3.setManufacturer("getter done3");
watch3.setAddress("12noon lane3");
watch3.setPhone("410-555-12123");
em.persist(watch3);select * from ORMCORE_WATCH ID MAKE MODEL 3 ontime3 round-and-round3
select * from ORMCORE_MAKER NAME PHONE ADDRESS MAKER_ID getter done3 410-555-12123 12noon lane3 3
select * from ORMCORE_OWNER CARDNUM NAME OWNER_ID 123-45-67893 john doe3 3