JPAでの多対多のリレーション

以前、このエントリーでJPAのリレーションについて説明しました。

今回は多対多について説明します。

Contents

1 テーブル構成
2 ソース
3 参考図書

テーブル構成

CDとアーティストが多対多で紐づているとします。

ER図で下記のようになっているとします。

ソース

CDのエンティティ

@Entity
@Table(name = "cd")
public class Cd  implements Serializable {
    
    private static final long serialVersionUID = 1L;
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "id")
    @Getter
    @Setter
    private Integer id;
    
    @Getter
    @Setter    
    @Column(name = "title")
    private String title;
    
    @Getter
    @Setter
    @Column(name = "price")
    private Integer price;
    
    @Getter
    @Setter
    @Column(name = "description")
    private String description;
    
    @ManyToMany( mappedBy = "cdList")
    private List<Artist> createdByArtists;    
    
}

@Entity

@Table(name = "cd")

public class Cd implements Serializable {

private static final long serialVersionUID = 1L;

@Id

@GeneratedValue(strategy = GenerationType.IDENTITY)

@Basic(optional = false)

@Column(name = "id")

@Getter

@Setter

private Integer id;

@Getter

@Setter

@Column(name = "title")

private String title;

@Getter

@Setter

@Column(name = "price")

private Integer price;

@Getter

@Setter

@Column(name = "description")

private String description;

@ManyToMany( mappedBy = "cdList")

private List<Artist> createdByArtists;

}

Artistのエンティティ

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.japrelation.entity;

import java.io.Serializable;
import java.util.List;
import javax.persistence.Basic;
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.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import lombok.Getter;
import lombok.Setter;

/**
 *
 * @author matsumoto
 */
@Entity
@Table(name = "artist")
public class Artist implements Serializable{
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "id")
    @Getter
    @Setter
    private Integer id;
    
    @Getter
    @Setter    
    @Column(name = "first_name")
    private String firstName;
    
    @Getter
    @Setter
    @Column(name = "last_name")
    private String lastName;
    
    @ManyToMany
    @JoinTable(name="jnd_art_cd", joinColumns = @JoinColumn( name = "artist_id"),
            inverseJoinColumns = @JoinColumn(name="cd_id"))
    private List<Cd> cdList;
    
}

* To change this license header, choose License Headers in Project Properties.

* To change this template file, choose Tools | Templates

* and open the template in the editor.

package com.japrelation.entity;

import java.io.Serializable;

import java.util.List;

import javax.persistence.Basic;

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.JoinTable;

import javax.persistence.ManyToMany;

import javax.persistence.Table;

import lombok.Getter;

import lombok.Setter;

/**

* @author matsumoto

@Entity

@Table(name = "artist")

public class Artist implements Serializable{

@Id

@GeneratedValue(strategy = GenerationType.IDENTITY)

@Basic(optional = false)

@Column(name = "id")

@Getter

@Setter

private Integer id;

@Getter

@Setter

@Column(name = "first_name")

private String firstName;

@Getter

@Setter

@Column(name = "last_name")

private String lastName;

@ManyToMany

@JoinTable(name="jnd_art_cd", joinColumns = @JoinColumn( name = "artist_id"),

inverseJoinColumns = @JoinColumn(name="cd_id"))

private List<Cd> cdList;

}

この場合Artist側が所有者になり、被所有者側のCdにはmappedByが付加されます。

両方にmappedByを書くと適切な結果が得られないようです。

データベースにアクセスするソース

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.japrelation.main;

import com.japrelation.entity.Artist;
import com.japrelation.entity.Cd;
import com.japrelation.entity.SampleOrder;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;

public class SampleFacade {
    
    private EntityManagerFactory fac;
    private EntityManager em;
    private EntityTransaction tx;
    
    public SampleFacade(){
        fac = Persistence.createEntityManagerFactory("com_japrelation_jar_1.0.0-SNAPSHOTPU");
        em = fac.createEntityManager();
        tx = em.getTransaction();
    }
    
    public List<Cd> getCdList(){
        return em.createQuery(" SELECT c FROM Cd c ",Cd.class).getResultList();
    }
    
    public List<Artist> getArtistList(){
        return em.createQuery(" SELECT a FROM Artist a ",Artist.class).getResultList();
    }
   
}

* To change this license header, choose License Headers in Project Properties.

* To change this template file, choose Tools | Templates

* and open the template in the editor.

package com.japrelation.main;

import com.japrelation.entity.Artist;

import com.japrelation.entity.Cd;

import com.japrelation.entity.SampleOrder;

import java.util.List;

import javax.persistence.EntityManager;

import javax.persistence.EntityManagerFactory;

import javax.persistence.EntityTransaction;

import javax.persistence.Persistence;

public class SampleFacade {

private EntityManagerFactory fac;

private EntityManager em;

private EntityTransaction tx;

public SampleFacade(){

fac = Persistence.createEntityManagerFactory("com_japrelation_jar_1.0.0-SNAPSHOTPU");

em = fac.createEntityManager();

tx = em.getTransaction();

}

public List<Cd> getCdList(){

return em.createQuery(" SELECT c FROM Cd c ",Cd.class).getResultList();

}

public List<Artist> getArtistList(){

return em.createQuery(" SELECT a FROM Artist a ",Artist.class).getResultList();

}

Mainのソース

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.japrelation.main;

import com.japrelation.entity.Artist;
import com.japrelation.entity.Cd;
import com.japrelation.entity.SampleOrder;
import java.util.List;

public class Controller {
    public static void main(String[] args){
        SampleFacade sf = new SampleFacade();
       
        //多対多
        List<Cd> cdList = sf.getCdList();
        //多対多        
        List<Artist> artistList = sf.getArtistList();
    }
}

* To change this license header, choose License Headers in Project Properties.

* To change this template file, choose Tools | Templates

* and open the template in the editor.

package com.japrelation.main;

import com.japrelation.entity.Artist;

import com.japrelation.entity.Cd;

import com.japrelation.entity.SampleOrder;

import java.util.List;

public class Controller {

public static void main(String[] args){

SampleFacade sf = new SampleFacade();

//多対多

List<Cd> cdList = sf.getCdList();

//多対多

List<Artist> artistList = sf.getArtistList();

}

参考図書

Beginning Java EE 6~GlassFish 3で始めるエンタープライズJava

http://www.amazon.co.jp/dp/4798124605

この本のP108～112を参考にしました。