如果一个表有多个主键（= =一般比较少）
8.4. 组件作为联合标识符(Components as composite identifiers)
先定义一个类OrderLineId
(实现接口，implems java.io.Serializable（把当前对象序列化的接口）)，
(实现接口，implems java.io.Serializable（把当前对象序列化的接口）)，
重写
为什么要序列化？内存满和集群化的时候用，具体百度(= =！其实我就是不懂)
里面有多个成员变量(字段(这些都是主键))
package com.zjx.hibernate;
public class StudentPK implements java.io.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;
}
@Override
public boolean equals(Object o) { //判断是否相等，相等就找它
if(o instanceof StudentPK) { //如果o是一个StudentPK对象
StudentPK pk = (StudentPK)o;
if(this.id == pk.getId() && this.name.equals(pk.getName())) {
return true;
}
}
return false;
}
@Override
public int hashCode() { //计算主键的hash码 if有多个对象 就直接找hash码
return this.name.hashCode();
}
}
然后在 类Student中 创建OrderLineId成员变量，set,get一下，
package com.zjx.hibernate;
public class Student {
private StudentPK pk;
private int age;
private String sex;
private boolean good;
public boolean isGood() {
return good;
}
public void setGood(boolean good) {
this.good = good;
}
/*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;
}*/
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public StudentPK getPk() {
return pk;
}
public void setPk(StudentPK pk) {
this.pk = pk;
}
}
其他都一样 就是hbm.xml配置文件改成如下
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping>
<class name="com.bjsxt.hibernate.Student"> <composite-id name="pk" class="com.zjx.hibernate.StudentPK">
<key-property name="id"></key-property>
<key-property name="name"></key-property>
</composite-id> <property name="age" />
<property name="sex" />
<property name="good" type="yes_no"></property>
</class> </hibernate-mapping>
如果是使用注释？
2.2.. 映射主键属性
下面是定义组合主键的几种语法:
- 将组件类注解为@Embeddable,并将组件的属性注解为@Id(比较少用)
- 将组件的属性注解为@EmbeddedId
- 将类注解为@IdClass,并将该实体中所有属于主键的属性都注解为@Id
对于EJB2的开发人员来说 @IdClass是很常见的, 但是对于Hibernate的用户来说就是一个崭新的用法.
组合主键类对应了一个实体类中的多个字段或属性,
而且主键类中用于定义主键的字段或属性和 实体类中对应的字段或属性在类型上必须一致.下面我们看一个例子:
@Entity
@IdClass(FootballerPk.class)
public class Footballer {
//part of the id key
@Id public String getFirstname() {
return firstname;
} public void setFirstname(String firstname) {
this.firstname = firstname;
} //part of the id key
@Id public String getLastname() {
return lastname;
} public void setLastname(String lastname) {
this.lastname = lastname;
} public String getClub() {
return club;
} public void setClub(String club) {
this.club = club;
} //appropriate equals() and hashCode() implementation
} @Embeddable
public class FootballerPk implements Serializable {
//same name and type as in Footballer
public String getFirstname() {
return firstname;
} public void setFirstname(String firstname) {
this.firstname = firstname;
} //same name and type as in Footballer
public String getLastname() {
return lastname;
} public void setLastname(String lastname) {
this.lastname = lastname;
} //appropriate equals() and hashCode() implementation
}
如上, @IdClass指向对应的主键类.
Hibernate支持在组合标识符中定义关联(就像使用普通的注解一样),而EJB3规范并不支持此类用法.
@Entity
@AssociationOverride( name="id.channel", joinColumns = @JoinColumn(name="chan_id") )
public class TvMagazin {
@EmbeddedId public TvMagazinPk id;
@Temporal(TemporalType.TIME) Date time;
} @Embeddable
public class TvMagazinPk implements Serializable {
@ManyToOne
public Channel channel;
public String name;
@ManyToOne
public Presenter presenter;
}
@IdClass(TeacherPK.class)；
那么就能使用TeacherPK的东西；
t.setId(1);
t.setName("t1");
t.setName("t1");
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