聯合主鍵關聯就是被關聯類的多個屬性聯合作爲主鍵,而關聯類中從數據庫表級別的映射關係來看,也有多個外鍵作爲聯合主鍵來關聯被關聯的對象。
首先做一個主鍵類(WifePK.java):
public class WifePK implements Serializable{
private int id;
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
注意:聯合主鍵類必須要實現Serializable接口,一般要重寫hashCode和equals方法,如果不實現這個接口,也可以正常生產數據庫,但是,我們在數據庫總做CRUD操作的時候,就會報錯。然後就是我們的實體類(Wife.java):
@Entity
@IdClass(WifePK.class)
public class Wife {
private int id;
private String name;
private int age;
@Id
public int getId() {
return id;
}
@Id
public String getName() {
return name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public void setId(int id) {
this.id = id;
}
public void setName(String name) {
this.name = name;
}
}
在Wife類頭部,我們通過@IdClass這個標識來制定所使用的主鍵類是哪個類。
最後就是我們的Husband.java類:
@Entity
public class Husband {
private int id;
private String name;
private Wife wife;
@Id
@GeneratedValue
public int getId() {
return id;
}
@OneToOne
@JoinColumns({
@JoinColumn(name="wifeid",referencedColumnName="id"),
@JoinColumn(name="wifename",referencedColumnName="name")
})
public Wife getWife() {
return wife;
}
public void setWife(Wife wife) {
this.wife = wife;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
在Husband中,我們通過@OnetoOne來指定這是一個一對一關聯,然後通過@JoinColumns來制定聯合主鍵所對應的聯合外鍵在Husband數據表中是如何關聯的。測試生成的數據庫語句如下所示:
09:22:09,987 DEBUG SchemaExport:377 -
create table Husband (
id integer not null auto_increment,
name varchar(255),
wifeid integer,
wifename varchar(255),
primary key (id)
)
09:22:10,130 DEBUG SchemaExport:377 -
create table Wife (
id integer not null,
name varchar(255) not null,
age integer not null,
primary key (id, name)
)
09:22:10,177 DEBUG SchemaExport:377 -
alter table Husband
add index FKAEEA401B4E7D3B35 (wifeid, wifename),
add constraint FKAEEA401B4E7D3B35
foreign key (wifeid, wifename)
references Wife (id, name)
09:22:10,400 INFO SchemaExport:268 - schema export complete
如上代碼所示:在Husband表中添加了wifeid,wifename作爲外鍵關聯到wife表中的聯合主鍵。