JPA 8장 (List collection mapping)

이번엔 List이다.

문제에 관련된 DB가 있다고 하자.

테이블은

question
id	varchar(10)
text	varchar(20)

question_choice
question_id	varchar(10)
idx	integer(10)
text	varchar(20)

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();
    }
}