인프런 커뮤니티 질문&답변

섹션 11-9 JPQL 함수에서, 사용자 정의 함수(group_concat) 구현 시 Hibernate(6.4.2.Final)버전을 사용할 때 가능한 방법 공유드립니다.

1. 강의에서 MyH2Dialect 클래스 구현하는 대신, FunctionContributor를 구현

public class MyH2FunctionContributor implements FunctionContributor {

    @Override
    public void contributeFunctions(FunctionContributions fc) {
        TypeConfiguration typeConfig = fc.getTypeConfiguration();
        SqmFunctionRegistry registry = fc.getFunctionRegistry();

        // ✅ 문자열 반환 타입을 직접 조회
        BasicType<?> stringType = typeConfig.getBasicTypeRegistry().getRegisteredType("string");

        // ✅ 사용자 정의 함수 등록
        registry.registerPattern(
                "group_concat",
                "group_concat(?1)",
                stringType
        );
    }
}

2. 서비스 등록 (META-INF/services/org.hibernate.boot.model.FunctionContributor)

jpql.MyH2FunctionContributor

3. 예시 쿼리

Team team = new Team();
team.setName("teamA");
em.persist(team);

Member member = new Member();
member.setUsername("관리자");
member.setAge(10);
member.setType(MemberType.ADMIN);

Member member2 = new Member();
member2.setUsername("사용자2");
member2.setAge(10);
member2.setType(MemberType.USER);


member.changeTeam(team);
em.persist(member);
em.persist(member2);

em.flush();
em.clear();

String query = "select group_concat(m.username) from Member m";
List<String> result = em.createQuery(query, String.class).getResultList();
for (String s : result) {
    System.out.println("s = " + s);
}

4. 결과 쿼리

Hibernate:

/* select

group_concat(m.username)

from

Member m */ select

group_concat(m1_0.username)

from

Member m1_0

s = 관리자,사용자2