100년 뒤 개발자 한승규입니다.

이번엔 List이다.

문제에 관련된 DB가 있다고 하자.

테이블은

그러면 question안에 객관식 보기인 question_choice들이 순서대로 들어가 있어야 할 것이다.

이런 경우에는 순서가 존재하기 때문에 저번에 사용한 Set을 사용할 수 없고, List를 사용해야 한다.

import jakarta.persistence.*;

import java.util.List;

@Entity
@Table(name = "question")
public class question {
    @Id
    private String id;
    private String text;

    @ElementCollection
    @CollectionTable(
            name = "question_choice",
            joinColumns = @JoinColumn(name = "question_id")
    )
    @OrderColumn(name = "idx")
    @Column(name = "text")
    private List<String> choices;

    protected question () {}

    public question(String id, String text, List<String> choices) {
        this.id = id;
        this.text = text;
        this.choices = choices;
    }
    //getter... settter
}

import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.EntityTransaction;
import jakarta.persistence.Persistence;

import java.util.List;

public class questionMain {

    public static void main(String[] args) {
        EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("jpabegin");
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        EntityTransaction entityTransaction = entityManager.getTransaction();

        try{
            entityTransaction.begin();
            question question1 = new question("1", "문제1", List.of("1번", "2번", "3번", "4번", "5번"));
            entityManager.persist(question1);
            entityTransaction.commit();
        }catch (Exception ignored){

        }

        try{
            question question2 = entityManager.find(question.class,"1");
            for(String choice : question2.getChoices()){
                System.out.println(choice);
            }
        }finally {
            entityManager.close();
        }

        entityManagerFactory.close();
    }
}

이렇게 Set과 똑같이 작성하지만, @OrderColumn을 추가해준다.

당연히 @Embedded도 사용이 가능하다.

import jakarta.persistence.Embeddable;

@Embeddable
public class choice {
    private String text;
    private boolean input;

    protected choice() {}

    public choice(String text, boolean input) {
        this.text = text;
        this.input = input;
    }

	//getter... setter...
}

import jakarta.persistence.*;

import java.util.List;

@Entity
@Table(name = "question")
public class question2 {
    @Id
    private String id;
    private String text;

    @ElementCollection
    @CollectionTable(
            name = "question_choice",
            joinColumns = @JoinColumn(name = "question_id")
    )
    @OrderColumn(name = "idx")
    private List<choice> choiceList;

    protected question2 (){}

    public question2(String id, String text, List<choice> choiceList) {
        this.id = id;
        this.text = text;
        this.choiceList = choiceList;
    }
	//getter... setter...
}

import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.EntityTransaction;
import jakarta.persistence.Persistence;

import java.util.List;

public class questionMain2 {

    public static void main(String[] args) {
        EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("jpabegin");
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        EntityTransaction entityTransaction = entityManager.getTransaction();

        try{
            entityTransaction.begin();
            question2 question1 = new question2("1", "문제1", List.of(new choice("1", false),
                    new choice("2", true)));
            entityManager.persist(question1);
            entityTransaction.commit();
        }catch (Exception ignored){

        }

        try{
            question2 question2 = entityManager.find(question2.class,"1");
            for(choice choice : question2.getChoiceList()){
                System.out.println(choice.getInput() + ", " + choice.getText());
            }
        }finally {
            entityManager.close();
        }

        entityManagerFactory.close();
    }
}

이런 테이블들이 있다고 해보자.

이렇게 job 안에 permission에 해당 하는 값들을 보관하고 있어야 한다.

import jakarta.persistence.*;

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

@Entity
@Table(name = "job")
public class job {
    @Id
    private String id;
    private String name;

    @ElementCollection
    @CollectionTable(
            name="job_perm", //job_perm 테이블 명
            joinColumns = @JoinColumn(name = "job_id") //job_perm 테이블의 job_id column
    )
    @Column(name = "perm") //job_perm 테이블의 permission column
    private Set<String> permissions = new HashSet<>();

    protected job() {}

    public job(String id, String name, Set<String> permissions) {
        this.id = id;
        this.name = name;
        this.permissions = permissions;
    }
	//getter... setter...
    public Set<String> getPermissions() {
        return permissions;
    }

    public void setPermissions(Set<String> permissions) {
        this.permissions = permissions;
    }
}

이렇게 내부에 Set을 만들고 @ElementCollection을 작성해준다.

한 번에 이해하기 힘들테니 바로 실행을 해보고 결과를 확인해보자.

import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.EntityTransaction;
import jakarta.persistence.Persistence;

import java.util.Set;

public class roleMain{
    public static void main(String[] args) {
        EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("jpabegin");
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        EntityTransaction entityTransaction = entityManager.getTransaction();

        try{
            entityTransaction.begin();
            job job1 = new job("1", "안녕", Set.of("11", "22"));
            entityManager.persist(job1);
            entityTransaction.commit();
        }catch(Exception ignored){

        }

        try{
            job job2 = entityManager.find(job.class, "1");
            for(String perm : job2.getPermissions()){
                System.out.println(perm);
            }
        }finally {
            entityManager.close();
        }

        entityManagerFactory.close();
    }
}

job을 persist 할 때 Set에 11, 22에 해당하는 값을 입력해주면

이렇게 job 테이블에 데이터 하나가 추가가 되고

job_perm 테이블에는 집합으로 넣었던 데이터 2개가 추가가 된다.

find로 조회할 때는

class에 작성했던 getPermission을 통해 for-each문으로 가져오면 된다.

당연히 Embeddable 타입도 가능하다.

이런 관계에서도 위와 비슷하게 @Embeddable 클래스만 만들어주고 동일 작업을 수행하면 된다.

import jakarta.persistence.Column;
import jakarta.persistence.Embeddable;

@Embeddable
public class information {
    @Column(name = "perm")
    private String permission;
    private String info;

    protected information () {}

    public information(String permission, String info) {
        this.permission = permission;
        this.info = info;
    }
    
    //getter... setter
}

import jakarta.persistence.*;

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

@Entity
@Table(name="role")
public class job2 {
    @Id
    private String id;
    private String name;

    @ElementCollection
    @CollectionTable(
            name="role_perm",
            joinColumns = @JoinColumn(name = "role_id")
    )
    private Set<information> informationSet = new HashSet<>();

    protected job2(){}

    public job2(String id, String name, Set<information> informationSet) {
        this.id = id;
        this.name = name;
        this.informationSet = informationSet;
    }
	//getter... setter...
    public Set<information> getInformationSet() {
        return informationSet;
    }

    public void setInformationSet(Set<information> informationSet) {
        this.informationSet = informationSet;
    }
}

이렇게 정상적으로 작동하게 된다.