Case 문

select, 조건절(where), order by에서 사용 가능

 

 

단순한 조건

@Test
    public void basicCase() {
        List<String> result = queryFactory
                .select(member.age
                        .when(10).then("열살")
                        .when(20).then("스무살")
                        .otherwise("기타"))
                .from(member)
                .fetch();

        for (String s : result) {
            System.out.println("s = " + s);
        }
    }

 

복잡한 조건

@Test
    public void complexCase() {
        List<String> result = queryFactory
                .select(new CaseBuilder()
                        .when(member.age.between(0, 20)).then("0~20살")
                        .when(member.age.between(21, 30)).then("21~30살")
                        .otherwise("기타"))
                .from(member)
                .fetch();

        for (String s : result) {
            System.out.println("s = " + s);
        }
    }

 

 

orderBy에서 Case 문 함께 사용하기 예제

 

예를 들어서 다음과 같은 임의의 순서로 회원을 출력하고 싶다면?
1. 0 ~ 30살이 아닌 회원을 가장 먼저 출력
2. 0 ~ 20살 회원 출력
3. 21 ~ 30살 회원 출력

NumberExpression<Integer> rankPath = new CaseBuilder()
 .when(member.age.between(0, 20)).then(2)
 .when(member.age.between(21, 30)).then(1)
 .otherwise(3);
List<Tuple> result = queryFactory
 .select(member.username, member.age, rankPath) .from(member)
 .orderBy(rankPath.desc())
 .fetch();
for (Tuple tuple : result) {
 String username = tuple.get(member.username);
 Integer age = tuple.get(member.age);
 Integer rank = tuple.get(rankPath);
 System.out.println("username = " + username + " age = " + age + " rank = "
+ rank);
}

 

Querydsl은 자바 코드로 작성하기 때문에 rankPath 처럼 복잡한 조건을 변수로 선언해서 select 절,
orderBy 절에서 함께 사용할 수 있다.

 

결과
username = member4 age = 40 rank = 3
username = member1 age = 10 rank = 2
username = member2 age = 20 rank = 2
username = member3 age = 30 rank = 1

 

 

 

 

 

출처 : 김영한 JPA 스프링 데이터 강의