hibernate联合主键生成机制（annotation方式）
这里记录hibernate中组合主键的annotation方式。
hibernate-annotations说明文档中有说到组合主键使用annotation的方式实现，如下几种
下面是定义组合主键的几种语法:
1. 将组件类注解为@Embeddable,并将组件的属性注解为@Id
2. 将组件的属性注解为@EmbeddedId
3. 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
第一种方式实例：
1.主键类，如下
package com.seed.lee.model;
import javax.persistence.Column;
import javax.persistence.Embeddable;
/**
* 这个类作为Person类的（组合主键）主键类
*
* @author Administrator
*
*/
@Embeddable //这里就是annotation文档中所说的，将组件类注解为@Embeddable
public class PeopleUionPKID implements java.io.Serializable {
private String firstName;
private String secondName;
@Column(length=20)
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
@Column(length=20)
public String getSecondName() {
return secondName;
}
public void setSecondName(String secondName) {
this.secondName = secondName;
}
@Override
public boolean equals(Object obj) {
if(obj instanceof PeopleUionPKID){
PeopleUionPKID pk=(PeopleUionPKID)obj;
if(this.firstName.equals(pk.firstName)&&this.secondName.equals(pk.secondName)){
return true;
}
}
return false;
}
@Override
public int hashCode() {
return super.hashCode();
}
}
2.与数据库表对应的类
package com.seed.lee.model;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
@Entity
public class Peopel {
PeopleUionPKID uionPKID = new PeopleUionPKID();
private int age;
private String sex;
private String job;
@Id //这里就是文档中所述的，并将组件的属性注解为@Id
public PeopleUionPKID getUionPKID() {
return uionPKID;
}
public void setUionPKID(PeopleUionPKID uionPKID) {
this.uionPKID = uionPKID;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Column(length=4)
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
@Column(length=20)
public String getJob() {
return job;
}
public void setJob(String job) {
this.job = job;
}
}
说明：除了代码中标为粗体的与普通的单主键类不同之外，其他都大同小异.
第二种方式比较简单
1.主键类，这个类不需要做任何的注解
package com.seed.lee.model;
import javax.persistence.Column;
/**
* 这个类作为Person类的（组合主键）主键类
*
* @author Administrator
*
*/
public class PeopleUionPKID implements java.io.Serializable {
private String firstName;
private String secondName;
@Column(length=20)
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
@Column(length=20)
public String getSecondName() {
return secondName;
}
public void setSecondName(String secondName) {
this.secondName = secondName;
}
@Override
public boolean equals(Object obj) {
if(obj instanceof PeopleUionPKID){
PeopleUionPKID pk=(PeopleUionPKID)obj;
if(this.firstName.equals(pk.firstName)&&this.secondName.equals(pk.secondName)){
return true;
}
}
return false;
}
@Override
public int hashCode() {
return super.hashCode();
}
}
2.数据表映射的类(只需要在主键类的引用中添加@EmbeddedId就可以)
package com.seed.lee.model;
import javax.persistence.Column;
import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.Id;
@Entity
public class Peopel {
PeopleUionPKID uionPKID = new PeopleUionPKID();
private int age;
private String sex;
private String job;
@EmbeddedId
public PeopleUionPKID getUionPKID() {
return uionPKID;
}
public void setUionPKID(PeopleUionPKID uionPKID) {
this.uionPKID = uionPKID;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Column(length=4)
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
@Column(length=20)
public String getJob() {
return job;
}
public void setJob(String job) {
this.job = job;
}
}
第三种方式,这种方式相对麻烦一点，据说这种是符合常人的编码规范的，所以有很多人用
1. 依然需要主键类，类中不需要注解任何的属性
package com.seed.lee.model;
import javax.persistence.Column;
/**
* 这个类作为Person类的（组合主键）主键类
*
* @author Administrator
*
*/
public class PeopleUionPKID implements java.io.Serializable {
private String firstName;
private String secondName;
@Column(length=20)
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
@Column(length=20)
public String getSecondName() {
return secondName;
}
public void setSecondName(String secondName) {
this.secondName = secondName;
}
@Override
public boolean equals(Object obj) {
if(obj instanceof PeopleUionPKID){
PeopleUionPKID pk=(PeopleUionPKID)obj;
if(this.firstName.equals(pk.firstName)&&this.secondName.equals(pk.secondName)){
return true;
}
}
return false;
}
@Override
public int hashCode() {
return super.hashCode();
}
}
2.数据表对应的类（这个类中需要将表的组合主键也记录成属性，并在所有的主键字段的get方法上注解@id，最后就是在类名上方注解
@IdClass(value=PeopleUionPKID.class)，PeopleUionPKID就是主键类的类短名）
package com.seed.lee.model;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
@Entity
@IdClass(value=PeopleUionPKID.class)
public class Peopel {
// PeopleUionPKID uionPKID = new PeopleUionPKID();
private String firstName;
private String secondName;
private int age;
private String sex;
private String job;
// @EmbeddedId
// public PeopleUionPKID getUionPKID() {
// return uionPKID;
// }
//
// public void setUionPKID(PeopleUionPKID uionPKID) {
// this.uionPKID = uionPKID;
// }
public int getAge() {
return age;
}
@Id
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
@Id
public String getSecondName() {
return secondName;
}
public void setSecondName(String secondName) {
this.secondName = secondName;
}
public void setAge(int age) {
this.age = age;
}
@Column(length=4)
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
@Column(length=20)
public String getJob() {
return job;
}
public void setJob(String job) {
this.job = job;
}
}
具体查看hibernate annotation的说明文档。