jpa双向一对多关联映射

最新推荐文章于 2020-12-23 12:06:01 发布

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最新推荐文章于 2020-12-23 12:06:01 发布

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CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/JAYIT/p/6941658.html

本文详细介绍了使用Java ORM框架进行实体关系映射的方法，包括Room类与Student类之间的多对一关系设置，以及如何在测试类中进行实体的添加和查询操作。通过具体的代码示例，展示了实体类的定义、字段映射、注解使用，以及持久化操作的实现。

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表结构

Room类

package auth.model;

import java.util.HashSet;
import java.util.Set;

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.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name="room")
public class Room {
	private int id;
	private String name;
	private Set<Student> students=new HashSet<Student>();
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	@Column(name="name")
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	@OneToMany(mappedBy="room",cascade=CascadeType.ALL,fetch=FetchType.EAGER)
	public Set<Student> getStudents() {
		return students;
	}
	public void setStudents(Set<Student> students) {
		this.students = students;
	}

}

Student类：

package auth.model;

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

@Entity
@Table(name="student")
public class Student {
	private int id;
	private String name;
	private int room_id;
	private Room room;
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	@Column(name="name")
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	@Column(name="room_id")
	public int getRoom_id() {
		return room_id;
	}
	public void setRoom_id(int room_id) {
		this.room_id = room_id;
	}
	@ManyToOne
	@JoinColumn(name="room_id",insertable=false, updatable=false)
	public Room getRoom() {
		return room;
	}
	public void setRoom(Room room) {
		this.room = room;
	}
}

测试类：

package auth.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.alibaba.fastjson.JSONObject;

import auth.dao.RoomDao;
import auth.dao.StudentDao;
import auth.model.Room;
import auth.model.Student;

@Service
public class RoomController {
	@Autowired
	private RoomDao dao;
	@Autowired
	private StudentDao dao1;
	public void add(){
		Room room=new Room();
		room.setName("教室3");
		dao.save(room);
		Student s=new Student();
		s.setName("小王1");
		s.setRoom_id(room.getId());//维护方是多的一方，所以不会主动关联一方的ID
		dao1.save(s);
		
	}
	
	public void query1(){
		Student student=dao1.findOne(5);
		String xx=JSONObject.toJSONString(student);
		System.out.println(xx);
		
	}
	public void query2(){
		Room room=dao.findOne(3);
		String xx=JSONObject.toJSONString(room);
		System.out.println(xx);
		
	}

}