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;
}

}