refactor: 환영 메시지 저장 및 조회 서비스 로직 변경

- NPE 방지를 위해 환영 메시지 저장 시 null 값이라도 DB에는 빈 리스트로 저장하도록 변경
- 서비스 레이어에서 필터링 하는 대신 프로젝션으로 바로 enum 객체를 가져올 수 있도록 변경

main/src/main/java/org/sopt/makers/crew/main/tag/v2/service/TagV2ServiceImpl.java

@@ -2,16 +2,15 @@
 
 import static org.sopt.makers.crew.main.global.exception.ErrorStatus.*;
 
-import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
-import java.util.Objects;
 
 import org.sopt.makers.crew.main.entity.tag.Tag;
 import org.sopt.makers.crew.main.entity.tag.TagRepository;
+import org.sopt.makers.crew.main.entity.tag.WelcomeMessageTypeProjection;
 import org.sopt.makers.crew.main.entity.tag.enums.TagType;
 import org.sopt.makers.crew.main.entity.tag.enums.WelcomeMessageType;
 import org.sopt.makers.crew.main.global.exception.BadRequestException;
-import org.sopt.makers.crew.main.global.exception.NotFoundException;
 import org.sopt.makers.crew.main.tag.v2.dto.response.TagV2CreateTagResponseDto;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
@@ -23,8 +22,6 @@
 @Transactional(readOnly = true)
 public class TagV2ServiceImpl implements TagV2Service {
 
-	private static final String JSON_VALUE_SEPARATOR = ",";
-
 	private final TagRepository tagRepository;
 
 	// 여기에 createGeneralMeetingTag 메서드도 추가하면 될 것 같습니다 나중에! (추후 일반 모임에 태그 추가 시 작성)
@@ -38,56 +35,31 @@ public TagV2CreateTagResponseDto createLightningTag(List<String> welcomeMessageT
 			throw new BadRequestException(VALIDATION_EXCEPTION.getErrorCode());
 		}
 
-		List<WelcomeMessageType> welcomeMessageTypeEnums = null;
-
-		if (welcomeMessageTypes != null) {
-			welcomeMessageTypeEnums = welcomeMessageTypes.stream()
-				.map(WelcomeMessageType::ofValue)
-				.toList();
+		if (welcomeMessageTypes == null || welcomeMessageTypes.isEmpty()) {
+			return saveTag(lightningId, List.of());
 		}
 
-		Tag tag = Tag.createLightningMeetingTag(TagType.LIGHTNING, lightningId, welcomeMessageTypeEnums);
-		tagRepository.save(tag);
+		List<WelcomeMessageType> welcomeMessageTypeEnums = welcomeMessageTypes.stream()
+			.map(WelcomeMessageType::ofValue)
+			.toList();
 
-		return TagV2CreateTagResponseDto.from(tag.getId());
+		return saveTag(lightningId, welcomeMessageTypeEnums);
 	}
 
 	@Override
 	public List<WelcomeMessageType> getWelcomeMessageTypesByLightningId(Integer lightningId) {
-		validateLightningId(lightningId);
-
-		String jsonWelcomeMessageTypes = tagRepository.findWelcomeMessageTypesByLightningId(lightningId)
-			.orElseThrow(() -> new NotFoundException(TAG_NOT_FOUND_EXCEPTION.getErrorCode()));
-
-		return parseWelcomeMessageTypes(jsonWelcomeMessageTypes);
-	}
-
-	private void validateLightningId(Integer lightningId) {
 		if (lightningId == null) {
 			throw new BadRequestException(VALIDATION_EXCEPTION.getErrorCode());
 		}
-	}
-
-	private List<WelcomeMessageType> parseWelcomeMessageTypes(String jsonWelcomeMessageTypes) {
-		List<String> values = splitAndTrimJsonValues(jsonWelcomeMessageTypes);
-
-		return values.stream()
-			.map(this::convertToWelcomeMessageType)
-			.filter(Objects::nonNull)
-			.toList();
-	}
 
-	private List<String> splitAndTrimJsonValues(String jsonWelcomeMessageTypes) {
-		return Arrays.stream(jsonWelcomeMessageTypes.split(JSON_VALUE_SEPARATOR))
-			.map(String::trim)
-			.toList();
+		return tagRepository.findByLightningId(lightningId)
+			.map(WelcomeMessageTypeProjection::getWelcomeMessageTypes)
+			.orElse(Collections.emptyList());
 	}
 
-	private WelcomeMessageType convertToWelcomeMessageType(String value) {
-		try {
-			return WelcomeMessageType.valueOf(value);
-		} catch (IllegalArgumentException e) {
-			return null;
-		}
+	private TagV2CreateTagResponseDto saveTag(Integer lightningId, List<WelcomeMessageType> welcomeMessageTypeEnums) {
+		Tag tag = Tag.createLightningMeetingTag(TagType.LIGHTNING, lightningId, welcomeMessageTypeEnums);
+		tagRepository.save(tag);
+		return TagV2CreateTagResponseDto.from(tag.getId());
 	}
 }