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这次大创有个需求，在数据库建表时发现，user表与project表的关系表 user_project的主键为复合主键：
CREATE TABLE user_project( user_id INT(20), project_id INT(20), timestamp VARCHAR (50), donate_money DOUBLE(10,2), PRIMARY KEY (user_id,project_id) );
在网上看了几篇博客，以及在spring boot干货群咨询（感谢夜升额耐心解答）过后总算是做出来了。这里做个总结，方便日后查阅。
正文
这里采用@IdClass注解的方式来实现复合主键；
思路
实现
复合主键类
package com.hzy.Model;
import java.io.Serializable;
/**
* Created by huangzhenyang on 2017/9/7.
* UserProject的复合主键类
*
* @Param userId
* @Param projectId
* @Param timestamp
* 由这三个共同组成复合主键
*/
public class UserProjectMultiKeysClass implements Serializable {
private Integer userId;
private Integer projectId;
private String timestamp;
//Constructor
public UserProjectMultiKeysClass() {
}
public UserProjectMultiKeysClass(Integer userId, Integer projectId, String timestamp) {
this.userId = userId;
this.projectId = projectId;
this.timestamp = timestamp;
}
//Setter and Getter
public Integer getUserId() {
return userId;
}
public void setUserId(Integer userId) {
this.userId = userId;
}
public Integer getProjectId() {
return projectId;
}
public void setProjectId(Integer projectId) {
this.projectId = projectId;
}
public String getTimestamp() {
return timestamp;
}
public void setTimestamp(String timestamp) {
this.timestamp = timestamp;
}
// ***重写hashCode与equals方法*** 划重点！
@Override
public int hashCode() {
final int PRIME = 31;
int result = 1;
result = PRIME * result + ((userId == null) ? 0 : userId.hashCode());
result = PRIME * result + ((projectId == null) ? 0 : projectId.hashCode());
result = PRIME * result + ((timestamp == null) ? 0 : timestamp.hashCode());
return result;
}
@Override
public boolean equals(Object obj){
if(this == obj){
return true;
}
if(obj == null){
return false;
}
if(getClass() != obj.getClass()){
return false;
}
final UserProjectMultiKeysClass other = (UserProjectMultiKeysClass)obj;
if(userId == null){
if(other.userId != null){
return false;
}
}else if(!userId.equals(other.userId)){
return false;
}
if(projectId == null){
if(other.projectId != null){
return false;
}
}else if(!projectId.equals(other.projectId)){
return false;
}
if(timestamp == null){
if(other.timestamp != null){
return false;
}
}else if(!timestamp.equals(other.timestamp)){
return false;
}
return true;
}
}注意：
复合主键类必须满足：
1. 实现Serializable接口;
2. 有默认的public无参数的构造方法;
3. 重写equals和hashCode方法。equals方法用于判断两个对象是否相同，EntityManger通过find方法来查找Entity时，是根据equals的返回值来判断的。hashCode方法返回当前对象的哈希码;
实体类
package com.hzy.Model;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.Table;
import java.io.Serializable;
/**
* Created by huangzhenyang on 2017/9/7.
*
*/
@Entity
@Table(name = "user_project")
@IdClass(UserProjectMultiKeysClass.class)
public class UserProject implements Serializable {
private double donateMoney;
private Integer userId;
private Integer projectId;
private String timestamp;
@Id
public Integer getUserId(){
return this.userId;
}
@Id
public Integer getProjectId(){
return this.projectId;
}
@Id
public String getTimestamp(){
return this.timestamp;
}
//getter and setter
public double getDonateMoney() {
return donateMoney;
}
public void setDonateMoney(double donateMoney) {
this.donateMoney = donateMoney;
}
public void setUserId(Integer userId) {
this.userId = userId;
}
public void setProjectId(Integer projectId) {
this.projectId = projectId;
}
public void setTimestamp(String timestamp) {
this.timestamp = timestamp;
}
@Override
public String toString() {
return "UserProject{" +
"donateMoney=" + donateMoney +
", userId=" + userId +
", projectId=" + projectId +
", timestamp='" + timestamp + '\'' +
'}';
}
}注意：
1. @IdClass标注用于标注实体所使用主键规则的类；
2. 在实体中同时标注主键的属性，比如这段代码中的userId,projectId以及timestamp ；
获取数据
方法一： 通过EntityManager获取，比如方法testUserProjectRepository()
方法二：通过Repository获取；这里记得在extends JpaRepository
