JPA关联关系表中加其他字段

用户5166330

发布于 2020-02-13 12:56:18

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发布于 2020-02-13 12:56:18

前言

JPA是Java Persistence API的简称，中文名Java持久层API，是JDK 5.0注解或XML描述对象－关系表的映射关系，并将运行期的实体[对象持久化]到数据库中。 Sun引入新的JPA ORM规范出于两个原因：其一，简化现有Java EE和Java SE应用开发工作；其二，Sun希望整合ORM技术，实现天下归一。（出自百度百科） JPA优点：上手快，使用简单。 JPA缺点：不适合关联关系复杂的项目。

正题

正常情况下使用@ManyToMany注解描述多对多关系时，JPA自动生成的表中是只包括两个对应实体的主键信息的。有些时候呢，就会遇到需要在关联表中加入想要的其他字段来辅助完成需求。比如部门与部门人之间关系。一个部门有多个人，一个又可以属于多个部门，一个人在不同的部门之间有不同的身份，在做展示的时候就涉及排序问题，一个人在不同的部门拥有不一样的排序。这里以老师，学生，老师对每个学生的印象分来进行编码。主体思路就是将@ManyToMany生成的关系表单独作为一个类，使用两个@ManyToOne来进行实现。一、老师实体类

package com.ysh.springboot.permissions.test;

import java.util.List;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

import lombok.Getter;
import lombok.Setter;

/**
 * 
 * @author ysh
 * @date 2020/01/03
 */
@Entity
@Table(name = "teacher")
@Getter
@Setter
public class Teacher {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "name")
    private String name;

    @Column(name = "age")
    private int age;


    @OneToMany(mappedBy = "teacher", fetch = FetchType.EAGER,cascade = CascadeType.ALL)
    private List<TeacherStudent> teacherStudents;


}

二、学生实体类

 package com.ysh.springboot.permissions.test;

import java.util.List;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

import lombok.Getter;
import lombok.Setter;
/**
 * 
 * @author ysh
 * @date 2020/01/03
 */
@Entity
@Table(name = "student")
@Getter
@Setter
 public class Student {

     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     private int id;
     
     @Column(name = "name")
     private String name;
     
     @OneToMany(mappedBy="student", fetch = FetchType.EAGER,cascade=CascadeType.ALL)
     private List<TeacherStudent> teacherStudents;

     
}

三、老师对学生印象分类

package com.ysh.springboot.permissions.test;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

import lombok.Getter;
import lombok.Setter;

/**
 * 
 * @author ysh
 * @date 2020/01/03
 */
@Entity
@Table(name = "teacher_student")
@Getter
@Setter
public class TeacherStudent {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name = "t_id")
    private Teacher teacher;

    @ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name = "s_id")
    private Student student;

    @JoinColumn()
    @Column(nullable=true,name="impression_score")
    private int impressionScore;


}

四、表生成结构